pu-foam which stays elastic?

Hi!

I have some steel construction, where I need a PU-foam bead of about

2" for insulation against water, to allow adaptation if the steel extend a little due heat and cold, the foam should stay a little elastic.

Is there a special foam for such purpose, and where could I order it over the net? Or will the standard foam from Loews in the red can with yellow cap also do it?

HC