What absorbs microwaves?

LEAD ABSORBS MICROWAVES
Sorry, but lead really doesn't effectively absorb microwaves - it is primarily reflective with only a trivial amount of "absorption". The term "absorption isn't quite quite correct - it really should be "attenuation" i.e. the microwaves are attenuated - lose their energy which can then be converted to heat - as they penetrate into a material. In that sense, water is a good microwave absorber, as are moist foods generally.In a broad sense, all materials are either primarily reflectors of the microwaves - such as aluminum; transparent to them - such as glass, paper or many plastics at lower temperatures; absorbers or attenuators - such as water, tea, moist foods, polar solvents such as nitrobenzene. However, all materials will exhibit all three properties but to a different extent - aluminum primarily reflects microwaves, but they do penetrate to a very tiny amount referred to as the skin-depth and so can caused a trivial amount of heat.