Ok, if you need something that doesn't get destroyed by anti matter but is destroyed under pressure why not just take a wall of DMND and put C4 on the other side. Antimatter has no effect, yet the C4 will explode under pressure, if you need it for bombs the C4 could trigger the bomb.
wikku9 I want a normal solid, not a wall. I also want it to break under pressure like goo, but if it was like brick or breakable metal that would be fine.