The MR21-0003-20 from MAST Technologies is a Microwave Absorber with Frequency 9 to 12 GHz, Thickness 0.040 Inch/1.0 mm, Thickness 0.040 Inch, Thickness (mm) 1.0 mm, Operating Temperature -60 Degrees F to 375 Degrees F. Tags: Cavity Resonance Absorber. More details for MR21-0003-20 can be seen below.