share an office and I'm thinking of putting some of this on the wall above each of their monitors to absorb their voices, so it doesn't echo all over the room when they're both on the phone.

I was going to buy the real stuff, but it's 3-4 x's more expensive and everything I read said it's only necessary in a recording setting, and won't really make a difference for the frequencies coming from a voice. Maybe I'll just buy the acoustical stuff to be safe, and because it looks kinda cool so it won't need to be covered.