The MR21-0009-20 from MAST Technologies is a Microwave Absorber with Frequency 2 to 5 GHz, Thickness 0.1 Inch/2.5 mm, Thickness 0.1 Inch, Thickness (mm) 2.5 mm, Operating Temperature -60 Degrees F to 375 Degrees F. Tags: Cavity Resonance Absorber. More details for MR21-0009-20 can be seen below.