MIL-PRF-24172B (SH)
4.5.6 Unicellularity. Unicellularity shall be determined in accordance with ASTM D 2856, procedure B.
4.5.7 Thermal conductivity. The thermal conductivity of the foamed material shall be determined in accordance
with ASTM C 177 at a mean temperature of 75oF (23.9ºC).
4.5.8 Resistance to oil. One specimen, approximating a 1-inch cube, shall be immersed in fuel oil in accordance
with MIL-PRF-16884. After 70 hours the specimen shall be removed, lightly blotted with paper toweling and compared to
an imaged specimen of similar size for evidence of softening, swelling, or dissolving.
4.5.9 Heat aging. The dimensions of two specimens, 1 inch by 4 by 4 inches, shall be recorded to the nearest 0.01
inch after being conditioned for 24 hours as specified in 4.5.1. The specimens shall then be placed in an oven for a 24-hour
period and the oven shall be maintained at 140 ± 1.8oF (60 ± 1oC). Upon completion of the exposure period, the
specimens shall again be conditioned for 24 hours as specified in 4.5.1 and the dimension re-measured to the nearest 0.01
inch. The average percent volume change for the two specimens shall be calculated and reported.
4.5.10 Humid aging. The dimensions of two specimens, 1 inch by 4 by 4 inches, shall be recorded to the nearest
0.01 inch after being conditioned for 24 hours as specified in 4.5.1. The specimens shall then be placed upon a shelf in a
container with a level of water sufficient to maintain an atmosphere of 90 to 100 percent relative humidity. The container,
loosely covered, shall then be placed in an oven for 7 days at a temperature of 140 ± 1.8oF (60 ± 1oC). Upon completion of
the exposure period, the specimens shall again be conditioned for 24 hours as specified in 4.5.1 and their dimensions re-
measured to the nearest 0.01 inch. The average percent change in each linear dimension of both specimens shall be
calculated and reported.
4.5.11 Water absorption. The water absorption of the foamed material shall be determined in accordance with
ASTM D 2842 and the average value for three specimens reported.
4.5.12 Water vapor transmission. The water vapor transmission shall be determined in accordance with ASTM E
96 desiccant method.
4.5.13 Flexural strength. The flexural strength shall be determined in accordance with ASTM C 203. An average
value for four specimens, 12 by 3 by 1-1/2 inches thick, shall be reported.
4.5.14 Low temperature aging. The volume change due to low temperature aging shall be determined at minus
o
40 F in accordance with 4.5.14.1 through 4.5.14.4. Three specimens, 1 inch by 3 by 3 inches, shall be used. The average
values obtained from the three specimens at the conclusion of each of the two cycles shall not exceed the maximum value
change as required by 3.5. After exposure to low temperature aging, the specimens shall be examined for evidence of
cracking.
4.5.14.1 Conditioning. Condition the test specimens at 73.4 ± 3.6ºF (23 ± 2ºC) and 50 ± 5% relative humidity for
not less than 40 hours prior to test in accordance with Procedure A of ASTM D 618.
4.5.14.2 Measurements of test specimens. The following measurements shall be made on conditioned test
specimens prior to testing, after reconditioning at the end of a test procedure, and at any stage as prescribed in the test
procedures:
(a) Weight - The weight within 0.05% if the specimen weighs 100 g or less, 0.1% if the specimen exceeds 100 g in weight.
(b) Dimensions - All dimensions to 0.001 inch (0.025 mm).
Specimens shall be brought to room temperature in an uncharged desiccator or equivalent closed container, which will
require 10 to 30 minutes. The specimen shall be weighed in less than 10 minutes after exposure to room conditions. The
dimensions shall be measured immediately after weighing the specimen.
4.5.14.3 Procedure. The test cycle shall be as follows:
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