Radiation-absorbent material
In materials science, radiation-absorbent material (RAM) is a material which has been specially designed and shaped to absorb incident radio frequency (RF) radiation (also known as non-ionising radiation), as effectively as possible, from as many incident directions as possible. The more effective the RAM, the lower the resulting level of reflected RF radiation.
Source: Wikipedia — Radiation-absorbent material (CC BY-SA 4.0)