Black foam is a conductive material

Beware : the black foam in the packaging of the board is a conductive material, with a resistance of approx. 5k. I suppose it is so to prevent electrostatic damages to sensitive components.

So it is a bad idea to keep the pins sunk in the foam when powering and using the board.

Yeah, this escaped me and I couldn't figure out why the board was acting so funny. It would take 2-3 minutes after plugging it into USB before it would enumerate and then it was brittle and could drop off USB randomly. Turns out that removing it from the foam fixes both problems. Whoops...

Does the foam work as a pressure sensor? Place the foam between two coins, measure the resistance while pressing.

Johan_Ha:
Does the foam work as a pressure sensor? Place the foam between two coins, measure the resistance while pressing.

So you were planning to make single use pressure sensor?
ESD foam is hard foam that will not go back to it’s original shape

Ok, then it's useless. Unless the resistance changes with just the pressure, not with the deforming. But I guess the resistance changes, if at all, only after the deforming happens.
But I once bought some components, which had these flexible foam pieces with pressure dependent resistance. Still have them somewhere.