Typical values for different materials are listed below.

Values are taken from IEC 60287-2-1 Ed.2.0 with following additions or deviations:

Symbol
$\rho_{\mathrm{j}}$
Unit
K.m/W
Related
$M_{\mathrm{j}}$
$U_{\mathrm{n}}$
Used in
$T_{\mathrm{3}}$
Choices
MaterialValue
PE3.5
HDPE3.5
PVC5.0 (Un <= 30kV)
6.0 (Un > 30kV)
POC5.0
PP4.5
SiR5.0
FRNC3.5
CR5.5
CSM9.1
CJ6.0
RSP6.0
BIT6.0