Since sponge is a kind of plastic (which is available according to VEXU manual),but we’re not sure if it’s really legal during competitions.
Sponge isn’t plastic: it is, you know, sponge.
I’d imagine the OP was talking about the polyurethane rectangle in your kitchen, not a dead animal.
@OP: I don’t think it would be legal as it contains materials other than plastic.
I don’t really mean sponge, I mean SPONGE