The polyiso product standards (ASTM C1289** and CAN/ULC-S704.1) require that manufacturers determine the thermal resistance under steady-state conditions in accordance with one of the following test methods:
- ASTM C177 (Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus).
- ASTM C518 (Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus).
- ASTM C1114 (Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Thin-Heater Apparatus).
**ASTM C1289 exclusively recognizes ASTM C1363 (Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus) as a fourth test method for determining steady-state thermal resistance.
In addition, both ASTM C1289 and CAN/ULC-S704.1 require that testing be evaluated in accordance with ASTM C1045 (Standard Practice for Calculating Thermal Transmission Properties Under Steady-State Conditions). Finally, under ASTM C1289, polyiso manufacturers must utilize ASTM C1058/C1058M (Standard Practice for Selecting Temperatures for Evaluating and Reporting Thermal Properties of Thermal Insulation).