At a 10 km/s orbital encounter even a dry sponge will have no problem penetrating the metal hull of a spacecraft, both will turn to plasma. This is what a collision with a 7 gram object does[1], a sponge is about 100 grams and it's softness won't matter when it's traveling at hypervelocity.

[1]https://en.wikipedia.org/wiki/International_Space_Station#/m...