The MR21-0008-20 from MAST Technologies is a Microwave Absorber with Frequency 2 to 5 GHz, Thickness 0.09 Inch/2.3 mm, Thickness 0.09 Inch, Thickness (mm) 2.3 mm, Operating Temperature -60 Degrees F to 375 Degrees F. Tags: Cavity Resonance Absorber. More details for MR21-0008-20 can be seen below.