12 Pack Acoustic Panels with Self Adhesive, 12" X 12" X 0.4" High Density Sound Proof Foam Panels for Walls, Soundproof Wall Panels, Brick Sound Absorbing Panels for Home Studio Office Decor - Black

https://a.co/d/0d1i4Y8p Here's a quick one I just found on Amazon, but there's lots of you search foam acoustic panels. As long as they do not have a hard back like a wood or plastic, you should be able to cut them with an exacto knife.