The question is pretty self-explanatory. What word can be used to describe something that blocks radio waves?

Edit: No, I am not looking for some easy word like "block" or "blocker". This is part of a project, and I need a word that sounds sophisticated.

Edit 2: Sentence example: Of those substances, _______ blocks radio waves most effectively.

I went to this website looking for an answer. I didn't find one... However, it explains what radio waves are pretty well, though.

https://www.scientificamerican.com/article/bring-science-home-block-radio-waves/

Thanks!