Resistant and resilient foam

[davis45]

I am looking for a type of foam (or other material) that would be suitable to dame up the bell of a pipe. I need it to be dense enough to be able to expand in the pipe when pushed in, but also able to contour to small variations. The foam also needs to be durable enough to be taken in and out a numerous times. The only other important specification is that it needs to be able to handle moisture, dirt, and small amounts of cement. I have looked on the Internet for types of foam, but it seems to be a plethora of them out there and I was starting to get overwhelmed. Pleas help.