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An experimental program on expanded and extruded polystyrene insulating materials has been undertaken to investigate the effects of moisture gain on thermal performance. The investigation had two major objectives:
(a) to assist in the development of test methods and techniques that address more realistically the subject of moisture effects on the properties of thermal insulations; and
(b) to develop a credible data base for typical polystyrene materials when subjected to a set of combined temperature, moisture gradient, and continuous time exposure parameters comparable to the most severe that could be foreseen for the continental United States.
In addition, more limited measurements were made on a phenolic foam product, and limited measurements of thermal performance of the materials were made at several mean temperatures encompassing those normally encountered in applications involving the building envelope. Finally, the result of an interlaboratory study on certain specimens from one of the investigations is presented. This was undertaken both to confirm the absolute thermal property values and to illustrate that the ASTM Test for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter (C 518–76) is capable of discriminating between very small incremental changes in thermal performance of the exposed specimens.
The results, which indicate relatively small effects under these conditions, are discussed in relation to those obtained in other studies involving moisture effects and to the probable behavior in the normal environment. The viability of the approach as a suitable standard testing technique is also discussed.
apparent thermal conductivity, expanded polystyrene, extruded polystyrene, moisture thermal performance, thickness effect, thermal insulation
Engineering director, Dynatech Scientific Inc., Cambridge, MA
Program manager, Fiber Materials, Inc., Biddeford, ME