referring to fig1 the padding material 10 comprises a sheet 12 of polyvinylchloride closed cell foam which is approximately 1 / 16 ( 0 . 16 cm .) thick and has a density in the range from about six pounds per cubic yard to about twenty four pounds per cubic yard , a density of eighteen pounds per cubic yard having been found particularly suitable . the closed cell foam , which is of medical grade , and is produced upon a restraining sheet or liner , in a manner known to the art , when removed from the liner after the material has set , has a macroscopically smooth skin surface , i . e ., one with very few hills and valleys that can interfere with the transit of moisture through the space between the foam surface and the skin of the patient . the sheet material , which may be prepared for commercial use in rolls in three or four inch widths , is perforated with a pattern of perforations of two different sizes , the larger perforations 14 preferably having a diameter of about 3 / 16 inch ( 0 . 48 cm .) and the smaller perforations 16 preferably have a diameter of about 1 / 8 inch ( 0 . 08 cm .). the padding material has a straight row of the smaller perforations spaced inwardly from each longitudinal edge by about 1 / 4 inch ( 0 . 64 cm .) and spaced apart approximately 1 inch ( 2 . 54 cm .) in the longitudinal direction . two additional rows 22 and 24 of small perforations are disposed centrally between rows 18 and 20 , these rows having a serpentine shape and the spacing between the perforations being roughly half that of the spacing in rows 18 and 20 . the larger perforations are also arranged in three longitudinally extending rows , a straight row 26 disposed along the central axis of the strip and two serpentine - shaped rows 28 and 30 disposed slightly inwardly from the rows 18 and 20 of small perforations . the perforations in straight row 26 are spaced apart approximately 1 inch ( 2 . 54 cm .) and the perforations in the other two rows are spaced approximately 1 / 2 inch ( 1 . 27 cm ) apart and in transverse alignment with the smaller perforations in tracks 22 and 24 . the serpentine pattern of the perforations helps take up the stress of elongation of the material and prevents tearing as it is stretched and wrapped upon itself as it is applied to the body . as seen in fig2 when the padding material is stretched in the longitudinal direction of the strip the circular perforations take on an oval shape having substantially the same area as the undistorted circular perforations . accordingly , whether the material is in relaxed condition , is slightly stretched , or is further stretched , the perforations have significant area for removal of moisture from the skin by vapor transmission . each perforation , whether the material is in its relaxed or stretched condition , is surrounded by an area of closed cell foam 12 considerably greater than that surrounding the slits in the padding material disclosed in u . s . pat . no . 4 , 294 , 240 . the wider spacing of the perforations , allowed by the extremely smooth surface of the closed cell pvc foam , contributes to greater strength and less risk of tearing , yet allows the padding , when applied longitudinally , to lie flat rather than roll at the edges . fig3 shows the padding material 10 applied over the knuckles of a human hand 32 and shows the perforations as having a slightly oval shape , indicating that the padding was stretched in the longitudinal direction during application . also shown in a cast 34 , preferably of the air permeable type , which has been partially cut away to expose the padding material 10 covering the knuckles . in use , a strip of padding is stretched as it is applied over the affected part of the body , normally with some overlap on itself , with the normal thickness of the padding under a cast being from one to two thicknesses of padding material . thicker applications may be made over large protruberances . the cast material is applied over the padding material in the usual manner . the closed cell pvc foam contains fda approved calcium stabilizers and is therefore non - toxic , and by reason of the way it is manufactured has a macroscopically smooth surface for application next to the skin . the contact angle betwen this extremely smooth skin surface of the closed cell pvc foam and the axis of a water molecule is smaller than the contact angle with the skin surface of closed cell polyethylene foam , for example , and this coupled with the smooth surface makes for a very rapid transit time for water across its surface . the material is water repellant at least to the extent that water penetrates the surface of the foam with difficulty . the closed cell pvc foam padding material having a density of eighteen pounds percubic yard conforms nicely to the shape of the body , including conforming to protuberances on the body such as elbows , knees , knuckles , etc ., and is resiliently compressible . when applied to the body the padding is wrapped upon itself and is somewhat compressed by such wrapping and by having the cast material applied over it . however , the compression does not cause permanent deformation of the padding , allowing the foam to resiliently expand should the injured member atrophy due to extended inactivity and continue to fill the void between the cast and the member to maintain a tight relationship therebetween . the padding material is essentially water repellent , but is water permeable by reason of the perforations therein which allow the vapor transmission of trapped moisture , both exogenous and inogenous , through the holes and out through the surrounding air permeable casting into the atmosphere . the improved padding material promotes the removal and dissipation of moisture in two ways : because of the smoothness of the foam surface next to the skin water actually runs down to and out the end of the cast when the encased extremity is shaken , and any entrapped moisture remaining is transported to the perforations both physically and by creating a gradient of partial pressure of water vapor by heating up the outside of the cast with a hair dryer , for example . as the areas defined by the perforations are heated , any moisture in those regions evaporates out through the air permeable casting material , causing a decrease in the partial pressure of water vapor in the perforations and drawing water vapor from under the areas of padding material surrounding the perforations to offset the decrease in partial pressure . the wider spacing of the perforations permitted by the favorable surface characteristics of the foam material gives the material greater strength and provides more padding than the slit configuration disclosed in u . s . pat . no . 4 , 294 , 240 . essential to the effectiveness of the described padding material is that it have the property of transporting moisture along the surface thereof that contacts the human skin , this property being a function of the electro - chemical contact angle between the foam surface and the axis of a water molecule which , in turn , depend on the density of the foam material , the electro - chemical contact angle increasing with increased density . on the other hand , if made too dense the foam material becomes less resilient and less conformable , thus placing an upper limit on the density . accordingly , although foam densities in the range between six and twenty - four pounds per cubic yard have produced acceptable results , with a density of eighteen pounds per cubic yard giving results superior to others tested , as a general rule the foam material should be made as dense as possible while retaining practically acceptable conformability and resilience .
perforated closed cell polyvinyl chloride foam padding material useful with an immobilizing orthopedic cast , said material being capable of transporting moisture along the surface thereof in contact with the human skin and of passing moisture such as water and perspiration from the human skin therethrough by vapor transmission , and being conformable and elastic in the longitudinal direction of the padding material .