CA1280880C - Synthetic down - Google Patents

Abstract

SYNTHETIC DOWN
A B S T R A C T

A synthetic replacement for down is described which comprises a blend of (a) 80 to 95 weight percent of synthetic, spun and drawn, crimped, staple, polyester microfibers having a diameter of from 3 to 12 microns; and (b) 5 to 20 weight percent of synthetic, thermo-plastic, staple macrofibers having a diameter of from more than 12, up to 50 microns.

Description

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"SYNTHETIC D0 , Field of the_lnvention The invention relates to a synthetic thermal insulator made of fibrous components and more particularly relates to such a material which is a replacement for down.

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srief Descri t_on of the Prior Art Representative of the prior art are disclosures given in the U.S. Patents 3,892,909; 4,042,740; 4,118,531, 6 4,134,167; 4,167,604; 4,364,996; 4,418,103; and U.
Application 2,050,818A.
The superiority of down as a lightweight clothing and bedding insulator has been recognized for centuries. In spite of several recent and very worthwhile advances in synthetic insulation, down has retained its status as the ultimate, lightweight insulator. Its insulating e~ficiency has not yet ~een equalled by a commercially-a~ailable product with the minimal density of a typical down filling. The loftiness that characterizes down and makes it such an e~fi-cient thermal barrier is unique in a further sense; it is recovered almost completely when a compressed down assembly ' ` ' , .

80~ 30 is aqitated. The loft-related virtues of down e~ist only under dry conditions, however, and loss of loft and an accom-panving deterioration in thermal performance when wet is the primary shortcoming of down in field applications.
We have discovered that a very particular blend of micro-fibers and macrofibers produces a synthetic alternative to down. The blend of the invention compares favorably to down or mixtures of down with .eathers as an insulator in that it will:
a. Provide an equally efficient thermal barrier, b. Be of equivalent density, c. Possess similar compressional properties, d. Have improved wetting and dr~ing characteristics, and e. Have superior loft retention while wet.
Background information relating to some of these performance characteristics is given ~elow.
Down sleepin~ bags and garments are extremely efficient th`ermal insulators because they have a very low internal heat transfer coefficient at all ~ulk densities when compared to the alternative materials presently employed. Moreover, e~perimental data also shows that the relative advantage of down becomes greater at the very'low bulk densities at which it is generally used. In the literature it is common prac-tice to compare the thermal performance of materials in terms of an 'apparent or effective thermal conductivity'. However ..

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it is e~trPmely important to realize that for fibrous insula-ting materials at the bulk densities that are of interest in personal cold-weather protection applications, the heat trans-fer is as much due to radiation and convection as it is to conduction in the fibers and the air. Consequently, improve-ments (decreases) in heat transfer by any of the three mechanisms of conduction, radiation and convection can potentially lead to performance improvements, and the present invention pays particular attention to the radiation companent of the heat transfer, and takes advantage-of a previously unappreciated characteristic of radiative transer.
In practice the balance between the three heat transport modes depends on the test or usage conditions as well as the sample st~ucture and con~iguration. For instance, when we measure the 'apparent' thermal conductivities of various webs at a certain temperature gradient and mean temperature ( a T = 50F, tm = 75F were selected as standard in our case) we have to remember that the results depend on the direction of heat flow. It is known that heat 1OW 'down' tests eliminate convection, so most samples were evaluated in this con~iguration. This simpli~ies the intexpretation of the e~perimental data since only two modes of heat transfer, namely conductlon and radiation are operative, and moreover since the conductive component is readily calculable ~or assemblies o these densities the critical role o~ radiation is easy to demonstrate.

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`` ~2~3013~0 Heat transfer ~y thermal conduction in a low density fibrous weh occurs by conduction across the air gaps and by conduction through and between fibers. The conduction can be treated theoretically as takinq place in a two-phase mixture of air and fibers - the air beinq the matrix and the fibers the included component. The standard mixture laws for two-phase systems apply and the overall conductivity kC
is given by C ftXa~kf,VF) where ka and kf are the conductivities of the air and solid fiber and VF is the volume fraction of fiber in the web assembly, such that V~ = PF~Pf~
and PF and P~ are the web and fiber material densities.
The form of the appropriate mixture law depends upon the geometry of the system and many attempts have been made to de-rive generalized representations of the functionality expressed by the expression of KC above. Examination of these results shows that the general orm for low density assemblies is ~ ~ k where ~ is a function o~ the geometry and ka c r c kf.
When VF is very small ( ~ 0.01), then a good approximation ~within 23) is simply kC ~ k and this approximation is qenerally adequate over the ran~e of densities -that is of interest in the applications consi-dered here. ~hus it is possible to conclude that the heat ." .

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trans~er bv conduction is essentially controlled by the con-ductivity of air, ka~ and this can not be reduced unless some form of evacuated svstem is used. Hence in order to reduce the heat transfer it is necessary to manipulate the radiation and natural convection conductivities. Since the test method-ology used is such that the convective co~ponen~ is s~ppressed, it is sufficient to focus attention on the radiative component.
We have seen that if the only (or the main~ heat trans-fer mechanism in low density fiber batts or webs was by heat conduction, we would expect the 'conductivity' to be constant - or to increase slightly with increased density This is not found to be the case, however, as shown by the experimen-tal data o~ Finc~ ], Baxter[ ], Fournier and Klarsfeld[ ], and Farnworth~4] for various materials and by Rees[51 for down. In fact, if the 'conductivity' is measured for the same material over a range of decreasing densities, it is seen that the conductivity decreases to a minimum and then the con-ductivity increases as density decreases, at a faster and faster rate.

[1] Finck, J.L., "Mechanisms o~ Heat Flow in Fi~rous Materials", J.N.B.S., 1930 ~2] Baxter, S., "The Thermal Conductivity of Te~tiles", Proc. Physics Soc., 1946 ~3] Fournier, D. and Xlars~eld, S., "Some Recent Experimental Data on Glass Fiber Insulting Materials, etc.", AST~ STP 544, 1974 [4] Farnworth, ~., "Mechanisms o~ Heat Flow Through Clothing Insulation", TRJ, 12, 1983 [5] Rees, W.M., Shirley Institute Con~erence on Comfort, ~280~80 The large conductivity at low densities is due to radiation if the heat flow direction is downwards or to radiation and natural convection when the heat flow direction is upwards.
E~perimental data for down at a ranqe of de~sities measured with the heat flow down is shown in Fiqure 1, and since there is no convective component the increase in heat transfer at low densities is clearly attributable to radiation. The direct plot of effective thermal conductivity as a function of density PF does not permit ready comparisons between materials since it is not easy to estimate relevant charac-terizing parameters from a curvilinear plot. However, it is found that a plot of the product ~PF against PF for low densitv fiber assemblies gives a straight line with a slope equal to the conductivity of air, ka, and the intercept o~
this plot on the kPF axis permits a quantification of the radiative heat transfer. This intercept, C, with units o ~stu in/hr ft2 F) (lb/ft3) in the British system is called the radiation parameter, and in order to produce the lowest possible heat transfer through a fiber assembly, this radia-tive parameter should be reduced to its minimum value~
Table I gives measured values of this parameter for a wide range of polymeric ~iber assemblies, together with details of the test materials, and ~igure ~ shows a plot o~
the radiation parameter against fiber diameter The general tendency that is clear from t~e experimental results is that the radiative parameter is reduced as the fiber diameter is decreased, with the result that the e~fective thermal resis-- - -;
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`- ~2t3~118~0 tance of the assembly is increased. It is eaually clear, however, that this reduction in fiber diameter is not benefi-cial without limit, since the samples of fiber assemblies containing microfibers show a sharp increase in radiation parameter. One of these assemblies is a commercial manifes-tation of the material described by ~auser tU.S. Patent 4,118,531) and Hauser's unequivocal statement ~col. 4, line 24~ that "The finer the microfibers in a web of the invention the better the thermal resistance" is demonstrably untrue.
It is interesting and significant that down, in which the fine fiber component has a diameter ranqe of 2.5 to 11.0 microns, appears to be situated at the minimum of the curve relating the radiation parameter to fiber diameter, and any synthetic polymeric fiber assembly attemptinq to emulate the thermal properties of down must also be so situated. One of the surprising and -novel aspects of the present invention is that it is demonstrated that this will not be p~ssible if the fiber assembly contains a si~nificant proportion of very fine fibers (here deEined as having diameters smaller than 3 microns), and since the slope of the curve is extremely steep on the small diameter side of the minimum, then only a small fraction of very fine fiber is sufficient to compromise the low value of the radiation parameter. In order to maintain a minimal value of the radiation parameter it is desirahle that the fiber assembly contain no more than 5~ of fiber material with a diameter smaller than 3 microns.

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~ 8 --TA~LE I
Values or the Radi2tion Par2~e~er C

Radiation Par~e~_,C
~nsit~~ Dia~ete- ~tu- n_ x lb x 10 P ~enier d(u) hr rt~ ~F ft3 f ~n 1~30 - ~.5-ll.0 4.8 A~ny Res. Co. PEr 1.38 0.5 . 7., 4.2 Teijin PET 1~38 0.8 10 5.2 B ~nt D102 PEr 1.38 1.6 13 7.0 ~elanese Polaryuard PET 1.38 S 23 lO.1 ~ollofil 808 PET 1.17 S.S 26 11.8 ~ollofil II PET 1.17 S.S 26 11.4 ~ollofil 91 PET 1.17 15 42 14.5 ~elt-blown pol olef~n 0.90 -- 1-3 9.4 Melt-~lown DEr 1.38 - 1-3 8.1 Hollor~ O= ~=.OS) 1.17 5.5 26 8.7 Ke~lar 49 1.4 1.~ 12 8.4 Black PET 1.38 4.5 21 13.0 : Examination of Figure 2 allows reasonable estimates of the upper le~els or fiber diameter permissible if t~e thermal properties of the assembly are to be maintained. r~ we set a limit of 0.075 units (atu in/hr ft2 F) llb/ft" for the radiation parameter, then the plot indicates ~hat the ~ulk of the fibers must lie within the diameter range of 3.0 to 12.0 microns and measurement of the thermal conductivi~y of a n~nber of webs confirms this conclusion.

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~ ~2~301~30 g The discussion p,esented above dealt with the physical parameters that control the thermal properties of low-density fiber assemblies; in order to produce a satisfactory down sub-stitute material it is necessary also to examine the mecha-nical behavior or such an assembly, and attempt to determine the optimum configuration for the assembly. This relates not onlv to the ability o' the assembly to maintain its preferred geometrical form but also gives some indication of the deqree of dif'iculty that might be encountered in establishing the assembly during the manufacturing process. Measurements of the thermal behavior indicate`that improved performance is generallv associated with small diameter fibers, bu~ that ; there is a lower limit of about 3 microns below whic~ the thermal performance begins to deteriorate significantly.
From a mechanical standpoint it is a matter of experience that e~ctremely fine fibers suffer from deficiencies or ri-giditv and strength that make them dificult to produce, manipulate and use, and there is thererore a minimum fiber diameter below which efforts to realize improved perfor~ance are not worthwhile. It is generally ac~nowledged that very fine fibers produce assemblies that exhibit very poor reco-very from compressive deformation. All the currently-avail-able commercial webs made from microdenier fibers exist only as dense structures, since they fall within ~he practical limits set by the fiber rigidity and are continuously sub-jected to consolidating forces throughout their use-life.
rt is interesting that this behavior is in marked contrast ,', - ~28C~ 0 to that of down, which is renowned for the renewable nature of its loft. It is likely that the unusual behavior of the down is related primarily to the svstem of nodes that exist on the ribrillae, which lead to a predisposition of a low density confi~uration under certain circumstances. The re-covery behavior is probably also aided by the presence of the small fraction of large diameter, stiffer filamentary material in the down assembly. Whatever the reason for the lofting potential of down, the maintenance of a low density is extremely important to the concept of lightweight warmth and is an essential feature of any viable down substitute material.
The problems associated with the mechanical stability of fine fiber assemblies are exacerbated in the wet condition since the sur~ace tension forces associated with the presence of capillary water are considerably greater than those due to gravitational forces or other normal use loading and they have a much more deleterious effect on the str~cture~ A
simple calculation suggests that the residual deformation in a wet assembly is likely to be at least one order of maqni-tude more severe than for a dry assembly due to gravitational loadin~ even under the best conditions. T~is calculation il-lustrates dramatically the extreme vulnerability to collapse of fine fibrous assemblies under capillary forces. ~oreaver the estimate unquestionably underestimates the situation since the Young's modulus of polymeric materials can typically be reduced by at least one order of magnitude when wet, which ... . . .. . . ........... ..
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~L2~3C18~30 will further increase the seriousness of the effect. Under wet conditions, anal~sis suggests that an assembly made of filaments with diameters below 10 microns could be e~tremely vulnerable to collapse under saturating condi-tions and expe-rimental evidence fully confirms this expectation both for down and for synthetic polymer assemblies. It is hiqhly desirable to have the filaments mzde from a polymer such as polyester, polyolefin or polyaramid whose mechanical proper-ties are not significantly reduced on wetting. Even if the polymer itself is insensitive to the effects of moisture it is also important to treat the fibers with a water-repellant finish. The down of commerce is usually treated in this way, and all th~ experimental data on down presented herein is for down so treated; similarly the synthetic polymer insulator materials described of this invention also require water repellant treatments to realize their full insulating and mechanical potential in the wet state.
The mechanical limitations of fine fiber assemblies discussed above present a serious conflict in light of the fiber diameters needed for improved thermal performance.
The range of requ1rements, both thermal and mechanical, that the down substitute must fulfill ma~e it almost inevitable that the assembly be made up from fibers of more than one diameter class: the small diameter fibers being responsible for the thermal performance o_ the assembly, with their dia-meter alling within the range that was discussed in the previous paragraph, namely between 3 microns and 12 microns, , . .. . .

~z~o~o and the large diameter fibers beinq responsible for the me-chanical per~ormance of the assembly. Just as there are limits to the diameter range of the smaller active diameter component of the blend, so there are reasonable limits that can be set on the large diameter component. We consider first the length ~f of filament of denier 3 t~at is con-tained in a unit cube of assembly of volume fraction VF and can show that an assembly of O.Ol volume fraction made up entirelv of l denier fibers contains approximately 104 cm of fiber. This is given by:
~ f = 9 x lO PfVF/D, and this e~pression demonstrates that if we attempt to improve the mechanical per~ormance of the assembly by the addition of large diameter fibers, we obviously have avail-able a shorter length of material: for example the addition of lO~ of 100 denier fiber involves only a lO centimeter length of material. In order to be effective, this length of fiber must be distributed uniformly within the l cm cube in a configuration that permits goad recovery from compres-sive loading in any direction, and such a distribution is essentially impossible to attain. Calculation indicates that the ma~imum fiber diameter that can be tolerated~as a recovery modifier in a low density assembly is approximately 30 denier, and smaller denier materials would be preferred for minimum impact on the volume fraction.

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The foregoing discussion addresses the issue of how much additional high denier material can be tolerated: it is equally important to attempt to estimate how much is needed.
The mechanism of deformation of the high-denier component will be principally bending and torsion, and in each of these modes of deformation the flexural riqidity of a circular filament varies as the fourth power of the diameter, and the stiffness of a fle~ural or torsional beam varies inversely as the third power of the length of the element. The deformation stiffness S of the assembly can be written S dC EI/~ 3 where ~ is the free length of fi~er between contact points.
Since I dC d4 and ~ oC d/VF it is possible to write:

S co dVF3 ' This expression shows the e~treme sensitivity of t~e stiffness of the assembly to the volume fraction, and the relative in-sensitivity to the fiber diameter, since the geometrical parameters of the assembly geometry offset the large changes in filament properties. This suggests that the use of high denier fibers is particularly valuable in very low density assemblies. The combined analysis suggests that the larger fiber in a low density mi~ed assembly should ideally have a diameter of approximately S0 microns in order to ma~imize the mechanical performance at a given density, and that a l0~ weight of mixture should be adequate.

~SUMMARY OF THE INVENTION
The invention comprises a thermal insulation material, ~hich comprise~ a blend of ..... . . . : . ~ . . .

280a~[) (a) 80 to 95 weight percent of spun and drawn, crimpedf staple, synthetic polymeric microfibers having a diameter of from 3 to 12 microns; and Ib) 5 to 20 weight percent of synthetic polymeric staple macrofibers having a diameter of from more than 12, up to 50 microns.
The insulation material of the invention is useful as a replacement for down and down/feather mixtures in clothing, bedding and like articles of insulation.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph plotting the effective thermal conductivity as a function of density for down insulation.
Figure 2 is a graphical representation plotting the radiation parameter against fiber diameter for a number of different fibers.

DETAILED DESCRIPT~ON OF ~HE PREFERRED
: EMBODIMENTS OF ~HE INVENTION
The thermal insulation material of the invention com-prises a blend of two different textile fibers. The fibers differ, essentially, in their diameters. The majority of the fibers in the blend are microfibers, with a diameter within the range of from 3 to 12 microns. The minor proportion of the blend is made up with macrofibers, i.e., fibers having a di~meter o more t~an lZ mic on~ p ~ abou~ ~ c ons ,, , ~

128C)B80 The microfibers employed in preparinq the bLended mate-rials of the preferred form of the invention are spun and drawn micro~ibers o~ a polyester, pre~erably oE polyethylene terephthalate, though other polymeric materials ma~ also be used in this invention. Methods of their manufacture are well known; see for example U.S. Patent 4,148,103. Advanta-geously the microfibers are drawn following their ex~rusion, to achieve a high tensile modulus, which is about 70 to 90 gms/denier ln the present example. A relatively high tensile modulus contributes to a high bending modulus in the material of the invention, and helps with the mechanical performance.
Advantaqeouslyt the macrofi~ers are also spun and drawn fi~:ers of a synthetic polymeric resln such as a polyester (preferably polyethylene terephthalate). We have also found macrofibers of polyaramids such as poly(p-phenylene tereph-thalamide) to be advantageous. Macrofibers of poly(p-~ ' ~
phenylene terephthalamine) are commercially available underthe trademark Kevlar.
,l~` The microfibers and preferably the macrofibers making ~, I
'~ up the thermally insulative blends of the invention are ~; crimped fibers slnce this makes it possible to produce low i density intimate blends of the two components. The tech-j~ niques for crimping fibers are well known and process details ,¦ need not be recited here. Advantageously the average crimp `' i number for both the microfibers and the macrofibers is within the range of from 8 to 20 crimps per inch. It is possible i to achieve satisfactory results with uncrimped macrofibers :~ :
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8(~ 80 but I believe that the presence o~' crimp on the micro~ibercomponent is critical to the success~ul operation o~ a low density, lofty assembly. The pre~ence of individualized opened and crimped microfiber also helps to make it possible to reestablish loft in the fiber assembly after compression or wetting, and hence improve the long term utility o~ the invention.
The microfibers and the macrofibers employed in the blends of the invention may, optionally, be lubricated.
Representative of lubricants conventionally used are aqueous solutlons of organopolysiloxanes, emulsions of polytetra-fluoroethylene, non-ionic surfactants and the like. Such lubricants may be applied to the fibers by spray or dip techniques we}l known in the art.
The macrofibers and the microflbers are blended toqether to form batts consisting of plied card-laps, although other fibrous forms may be equally suitable. The card laps, or out-put webs from a carding machine, are intimate blends of spun-and-drawn microfibers~and macrofibers.; The batts are adYan-tageously made to achieve densities comparable to the densi-ties characteristic of down, i.e., on the order of less than 1.0 Ib/cubic oot, tvpically around 0.5 lb/cubic foot.
The follow1nq examples describe the manner and process ~1 ~ of making and using the invention and set forth the best mode contemplated by the inventor for carrying out the invention but are not to be construed as limiting. ~here reported, the following tests were employed:

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~2 !3~)~8~) Densitv The volume o~ each insulator sample was determined by ~ixing two plana~ 9ample dimensions and then measuring thickness at 0.002 lb/in. 2 pressure. The mass of each sample divided by the volume thus obtained is the basis for densitv values reported herein.
¦ Th~ckness was measured at 0.002 lb/in.1.
AD~arent thermal conductiv tv was measured in accord ~ith the p}ate/sample/plate method described by ASTM Method C518.

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Compressional Strain Strain at 5 lbJin.', which was the ~; maximum strain in the compressional recovery test sequence, was recorded for each test.
Compressional Recovery and Work of ComDression and Recovery Secti~on 4.3.2 o Mllitary Specific-ation MIL-B-41826E describes a compressional-recovery test technique for fibrous batting that was~adapted for this work. The essential ; di'~erence between the Military Speci'ication method and the one employed is the lower pres~sure at which 1nitial~th1ckness and recovered-to-thic~ness~were measured. The , ;l ~ measuring pressure inlthe speci-ication is : ~ ~
~ ~ 0.01 lb/~in~', whereas 0.002 lb/in~' was used :
~ ~ ~ in this work.
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.. : , ~8088 Water Absorption Capacity AS~M Method D1117 provided the starting point for development o~ the water absorption- capacLty and absorption-time test used. However, wetted- sample weighinss were made at frequent intervals during the first six,hours o~ immersion and another weighing was made after twenty-Four hours ~Method D11l7 requires only one wetted~
samp1e weighing). A unique sample-holder and a repeatable technique for draining excess water prior to each weighing were adopted after some in~tial experimentation.

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~ ~ Dryin~ Time After each absorption capacity test, :
weighings w re made at one-half hour intervals as the~sample air-dried on a wire rack in a 70F., 65~ r.h. atmosphere.
The down used throughout t~e examples was actually a down/fea-hers mixture,~80t20 by weight, per MIL F-43097G, Type II, Class I. ~his mixture is commonly and commercially referred to as "down" and is~often~re erred to as "down"

: hereln.
Example 1 A quantity of spun~and drawn l.2 inch long microfibers I having a diameter of 7.5 microns is provided. The fibe~ are lubricated w1th a silicone finish. The spun-and-drawn micro-fibers are polyester~and have been drawn to achieve a rela-:
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, ~2RO~F30 tively high tensile modulus ~60-90 grams/denier), which co~tributes significantly to a high bending modulus. A~te~
drawing they have been crimped, cut into staple and thoroughly opened, or separated, in~a card. The high bending stiffness and crimp are essential characteristics which provide and help to maintain advantageous loft. The average crimp fre-quency is 14/inch and the average crimp amplitude is 0.04 inches. Loft and compressional characteristics are improved further through the blending wlth 10 percent by weight of macrofibers of the ~ame polyester ~polyethylene terephthalate) having diameters of 25.5 microns. The macrofihers are lubricated with a silicone finish and are characterized in part by a staple length of 2.2 inches, an average crimp frequency of 8.5linch and a crimp ampiitude (average) of 0.06 inches. The blend is carded into a batt. The physical properties of the batt are shown in Table II, below, compared to a batt of down.

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Example 2 ; ~ ~The procedure of Example 1, supra., is repeated except that the macrolber as used thereln 5 replaced with 20 percent by weight of uncrimped poly(p-phenylene terephthala-mide) fibers having a diameter of 12 microns, a length of :
3.0 inches, and a silicone lubricant finish. The physical :
! ~ characteristics of the material formed are given in Table II

below.
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~2B08~30 TABLE II
____ Apparent thermal co~ductivity 0.180 0.281 0.271 (Btu-in./hr-~t2-F) m erm~l cond. test density (lb/Et3)0.45 0.47 0.48 Minimum density (lb/ft') 0.24 0.25 ~.25 Comp. strain at S Ib/in.l~3)b 95 96 92 Comp. reoovery from 5 Lb/in.~(~)b 102 112 112 Work to compress to S lb/in.a 4.91 3.49 3.57 (~in.l ResilienceC 0.53 0.62 0.60 Wettinq during Immersi n .
Water ~ sorption after 20 min. 1.16 2.16 1.41 Density after 20 mQn wetting 0.48 0.50 O.S1 wetting (Ib/ft~) -Water absorption after 6 hr ~x dw)3.75 5.15 3.44 l :
'~ Density after 6 hr wetting llbi~t')3.55 0.94 1.02 . 1 .
Drvin~ after 24 hrs. Water Im~ersion ~ ',~ ght after 30 min drying (x dw)3.88 4.83 3.29 j ~ Density aft~r 30 min drying (lb~ft3) 5.2lJ 0.95 0.90 Weight after 6 hr~drving (x dw) 2.45 1.68 l.Oi Density after 6 hr drying (Ib~ft3)3.20 0.41 0.44 ~j :
I ~ a. Heat flow down. 2.06 in~ specimen thickness.
b. Gauge l~ gth: 2.00 inches: density at 2.00 inch thickness was 0.50 Ib/ft3.
c. Resilience equals: work-o~-recovery divided bv work-to-compre d. x dw: times dry-weight , : ' .
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It can be seem from the above Table II that, in most instances, both examples of the invention offer per~ormance equivalent to that o~ the down/feathers mixture, and that the values of compressional recovery, work to compress, and resilience measured for both embodiments represent some improvement over those of down. Improvement of perhaps greater significance is apparent through comparison of densities at the "6 hr wetting," "30 min drying" and "6 hr drying" intervals in the wetting/drying cycle. The much lower densities measured for the two forms of the invention show ~hat it retains its loft while wet and, most probably its lnsulating value, to a far greater degree than does down. Resistance-to-wetting and resistance to loss-of-loft while wet are inherent advantages of the fiber combination described. The hydrophobic nature of polyester and the 1:
¦ microporous structure of the insulators are assumed to contribute to these desirable characteristics.
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Claims (9)

1. A synthetic fiber batt thermal insulator material, which comprises a blend of (a) 80 to 95 weight percent of spun and drawn, crimped, staple synthetic polymeric microfibers having a diameter of from 3 to 12 microns; and (b) 5 to 20 weight percent of synthetic polymeric staple macrofibers having a diameter of from more than 1;2, up to 50 microns, said batt having the following characteristics:
a radiation parameter defined as the intercept on the ordinate axis at zero density of a plot of kCPF against PF less than 0.075 (Btu-in/hr-ft2-oF) (lb/ft3) a density PF from 0.2 to 0.6 lb/cu ft and an apparent thermal conductivity KC measured by the plate-to-plate;method according to ASTM C518 with heat flow down of less than 0.5 Btu-in./hr ft2oF.

2. A material as claimed in claim 1 having in the dry state a compressive strain of at least 90% under a compressive stress of 5 lbs/square inch and a long-term compressive recovery of at least 95% after removal of this stress.

3. A material as claimed in claim 1 in which at least one of the fibrous components is treated with a water repellent finish.

4. A material as claimed in anyone of claims 1 to 3 in which at least one of the fibrous components is treated with a lubricant finish.

5. A material as claimed in anyone of claims 1 to 3 in which the crimp in the microfibers is within the range 8 to 20 crimps per inch.

6. A material as claimed in anyone of claims 1 to 3 in which the synthetic polymeric fibers are one or more of poly(ethylene terephthalate), and polyaramide.

7. A material as claimed in anyone of claims 1 to 3 in which the synthetic polymeric fiber is poly(p-phenylene terephthalamide).

8. A material as claimed in anyone of claims 1 to 3 in which the microfiber component is a polyolefin.

9. A material as claimed in anyone of claims 1 to 3 in which the macrofibers are crimped.