eccosorb+hfss
Hi,
If you don't know material properties of your absorber (and at the frequency you work), it's very difficult to have a good idea of the impact on your circuit or cavities.
There are a lot of absorbers, with very different properties.
In a general way, at RF frequencies:
Er value between 8 to 30 with dielectric loss tangent between 0 to 0.5
Mur value close to unity with magnetic loss tangent between 0.5 to 1.5
All absorbers I know are material in which magnetic losses are dominant.
It's fo EMI Shielding, Isolation, Resonant Cavity suppression.... ?
Each applications have its material. See datasheet of suppliers.