Do you understamd what happens when a material like graphene absorbs microwaves?
"Shielding electronic devices with a barrier that simply reflects incoming microwave radiation only shifts the electromagnetic pollution problem elsewhere. The research focus is therefore on developing EMC coatings that absorb rather than reflect microwaves, with a practical emphasis on layers less than a thousandth of a millimetre thick.
A team of physicists led by Philippe Lambin from the Université de Namur in Belgium has found that a graphene plane can provide an effective absorbent shield against microwaves. "
https://www.sciencedaily.com/releases/2015/03/150323075813.htm