but in fact, really, nothing is a total barrier or a total insulaor. hydrogen goes through just about anything we use to contain it, eventually leaking out - just measure outside a hydrogen container or special hydrogen hose. cosmic rays go through anything (I think).
But a brick wall only stops some things. Neutrinos will pass through it. Radio waves will pass through it. Neutrons will probably pass through it. Even gamma rays will pass through it with some probability. Muons will pass through it. Neutral K mesons will pass through it.
For the most part, a brick wall will stop significantly massive objects, and little else. (If you don't like the fact that it stops some frequencies of light, then we'll use a clear material.) What else do you want a "gravity insulator" to do?