That seems intuitive, though. EM radiation is either reflected or absorbed, and optimizing for that requires both a pretty complex understanding of RF behavior and generally knowing that materials are generally radiopaque and radiolucent at different frequencies and wattages.

Sometimes we're trying to keep things (eg- information) outside from getting in, and other times we want to prevent things inside from getting out. There are practices to optimize for both that don't rely on "blocking".