Polystyrene Foam Insulation in Long-Term Building Applications – Effective R-values
Page 12
The best fit of the ASTM C578 data leads to equations that can be used to determine the temperature adjustment
factor at temperatures other than 75°F (24°C):
Temperature
ASTM C578 Material Type
EPS XPS
II IX X IV
20°F (-7°C) 1.16 1.15 1.13 1.13
30°F (-1°C) 1.13 1.12 1.11 1.11
40°F (4°C) 1.10 1.10 1.08 1.08
50°F (10°C) 1.08 1.07 1.06 1.06
60°F (16°C) 1.05 1.05 1.04 1.04
70°F (21°C) 1.02 1.02 1.02 1.02
80°F (27°C) 0.99 0.99 0.99 0.99
90°F (32°C) 0.96 0.97 0.97 0.97
100°F (38°C) 0.94 0.94 0.95 0.95
110°F (43°C) 0.91 0.91 0.93 0.93
Table 6. F
TEMP
for EPS and XPS at Temperatures Between 20°F (-7°C) and 110°F (43°C)
Table 6 provides the temperature adjustment factor, F
TEMP
, using Equations 3 through 5 for mean temperatures from
20°F (-7°C) to 110°F (43°C).
For Type II EPS:
Equation 3 F
TEMP
= 1.214 – (0.0028 x Mean Temperature°F) or F
TEMP
= 1.125 – (0.0050 x Mean Temperature°C)
For Type IX EPS:
Equation 4 F
TEMP
= 1.204 – (0.0026 x Mean Temperature°F) or F
TEMP
= 1.119 – (0.0048 x Mean Temperature°C)
For Type X or IV XPS:
Equation 5 F
TEMP
= 1.172 – (0.0022 x Mean Temperature°F) or F
TEMP
= 1.100 – (0.0040 x Mean Temperature°C)
