Thermal Resistance (R) is a measure of resistance to heat flow through a given thickness of material (related directly to the R-value). Thermal resistance is determined by taking the thickness of a sample and dividing it by its thermal conductivity. Thermal resistivity is the inverse of the thermal conductivity. Thermal resistivity and R-value are sometimes used interchangeably, however, thermal resistivity differs in that it is a material property (i.e. independent of thickness).
Thermal resistance is specifically used to compare the performance of insulation products. Insulation can take the form of foams, aerogels, or other thermal barrier materials. R-value is often used to quantify single layered samples but can also be applied to layered structures such as those in vacuum insulation panels.
A range of both transient and steady state methods are available for testing at TAL. The Heat Flow Meter (HFM) is considered the gold standard method for determining the thermal resistance of insulation. HFM allows us to measure the thermal conductivity from -10 to 60 °C, and we offer services with multi-temperature point measurements, within ASTM C518-17 specifications (see general HFM design schematic below). The Modified Transient Plane Source (MTPS) is well-suited for a wide range of materials. Specifically, the high-temperature MTPS configuration is ideal for testing insulations used in elevated temperature applications. Learn more about our equipment for thermal conductivity and thermal resistance testing here.
We offer MTPS and HFM testing for the thermal resistance of insulation, foams and other materials. Below is a selection of the measurement requirements for thermal resistance testing services.
| Measurement range | 0.002 – 1.0 W/mK |
| Sample size | 100 x 100 mm or 300 x 300 mm. Min. thickness of 5 mm. |
| Temperature range | -10 – 60 °C |
| Material types | Foams, aerogels, polymers and vacuum insulation pannels |
| ASTM/ISO/EN Standards | ISO 8301, ASTM C518, EN 1946-3, EN 12664, EN 12667, EN 12939 |
| Measurement range | 0 – 0.150 W/mK |
| Sample size | Min. diameter of 18 mm. Min thickness is dependent on the thermal conductivity. For materials under 1W/mK, a minimum thickness of 1 mm is suggested. |
| Temperature range | 25 – 500 °C |
| Material types | Foams, solids and powders |
| ASTM/ISO/EN Standards | ASTM D7984 |
Other methods may be available. Contact us at info@thermalanalysislabs.com or call (506) 457-0498 to discuss.