The values for relative permittivity, known as dielectric constant, of insulation are taken from standard IEC 60287-1-1 Ed.2.1 where available with the following additions:

Symbol
$\epsilon_{\mathrm{i}}$
Unit
-
Related
$M_{\mathrm{i}}$
$U_{\mathrm{n}}$
Used in
$C_{\mathrm{b}}$
$c_{\mathrm{SI}}$
Choices
MaterialValue
PE2.3
HDPE2.3
XLPE2.5
XLPEf4.0 (Un <= 30kV)
3.0 (Un > 30kV)
PVC8.0
EPR3.0
IIR4.0
PPLP2.8
Mass4.0
Oil3.6 (Un <= 150kV)
3.5 (Un > 150kV)
PP2.27
SiR3.2
SiR2.95