foam for window seat (Near NE Heights, can pick up)

Need 21 x 31 ish, can combine or cut if anyone has leftover foam from a project or bed topper I can cut. Trying to make a soft window seat without consuming new resources. Also trying to soundproof a room so anything foam will help me. Thanks! (I apologize ahead of time if not immediately responsive- not using an ap -but I will check my computer a few times a day promise).