Yesterday I was curious how the butt cap trap door feature works on one of my old rackets. Luckily I didn't break it as I wasn't aware they slide up and down instead of opening like a hinge as I expected. After I got it off, I looked inside the handle. One side was filled with what looks like some sort of foam or maybe it's silicon that everyone talks about. The other side is empty. Not clean empty, more like someone removed the foam as there are remnants left. Why would someone remove part of the filling? For customizing the balance? Would that really make enough of a difference to be worth the effort? Should I fill the empty chamber with great stuff, silicon, or leave it as is? I don't hear any rattling, but the racket could use a little more weight in the handle even with the leather grip and lead tape strips (5 grams) I have now. But I can't imagine filling the chamber would add any significant weight to the handle. Anyone run into this situation? And how did you "handle" it? Thanks for all replies. BTW This is a POG LB I bought here from the classifieds.