Standard Test Method for Measuring Compressive Properties of Thermal Insulations

The compressive resistance is determined on either rigid board or blanket insulation. Specimens can be square or circular with a preferred width or diameter of 6". Testing of four specimens per type/brand is recommended by ASTM.

$300 per test of 4 specimens


Significance and Use

4.1 In providing Procedures A and B, it is recognized that different types of thermal insulation will exhibit significantly different behavior under compressive load. Data must usually be obtained from a complete load-deformation curve, and the useful working range normally corresponds to only a portion of the curve. The user is cautioned against use of the product in the range beyond which the product is permanently damaged or properties are adversely affected.

4.2 Load-deformation curves provide useful data for research and development, quality control, specification acceptance or rejection, and for other special purposes. Standard loading rates shall not be used arbitrarily for all purposes; the effects of impact, creep, fatigue, and repeated cycling must be considered. All load-deformation data shall be reviewed carefully for applicability prior to acceptance for use in engineering designs differing widely in load, load application rate, and material dimensions involved.


1. Scope

1.1 This test method covers two procedures for determining the compressive resistance of thermal insulations.

1.1.1 Procedure A covers thermal insulations having an approximate straight-line portion of a load-deformation curve, with or without an identifiable yield point as shown in Figs. 1 and 2. Such behavior is typical of most rigid board or block-type insulations.

C-165 Figure 1

FIG. 1 Procedure A-Straight Line Portion with Definite Yield Point

C-165 Figure 2

FIG. 2 Procedure A-Straight Line Portion but no Definite Yield Point

1.1.2 Procedure B covers thermal insulations that become increasingly more stiff as load is increased, as shown in Fig. 3. Such behavior is typical of fibrous batt and blanket insulations that have been compressed previously to at least the same deformation by compression packaging or mechanical softening.

C-165 Figure 3

FIG. 3 Procedure B-Increasing Stiffness

1.2 It is recognized that the classification of materials under Procedures A and B shall not hold in all cases. For example, some batt or blanket materials that have not been compression packaged will exhibit behavior more typical of Procedure A for their first loadings. Also, some higher density fibrous insulation boards that have been precompressed will exhibit load-deformation curves more typical of Procedure B. There will also be thermal insulations with load-deformation curves that follow none of the three types shown here; that is, curves with no straight-line portion, curves with compaction areas, and curves that change from negative to positive slope.

1.3 This test method does not cover reflective or loose fill insulations.


Copyright Notice

Extracted, with permission, from ASTM C165 Standard Test Method for Measuring Compressive Properties of Thermal Insulations, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the standard may be purchased from ASTM International, phone 610-832-9555, e-mail:, website:


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