According to standard IEC 60287-2-1 Ed.2.0

Symbol
$U_{\mathrm{d}}$
Unit
K.m/W
Related
$M_{\mathrm{d}}$
Used in
$T_{\mathrm{4i}}$
Choices
MaterialValue
Metal5.2
Fibre5.2
Cem5.2
PVC1.87
PE1.87
PP1.87
Earth1.87
WPE0.1