Does Open Cell Soft Foam Absorb Water?

No; it looks like a sponge but it is actually hydrophobic, i.e. it repels water. If placed in water it will float, and on removal, it will dry rapidly with no loss of insulating properties. If you ever have a roof leak or plumbing leak in your home which would soak the insulation, the water will ultimately settle out of and it will not damage the foam. We can't say the same for other insulations. Water breaks down the glue in a fiberglass batt so the batt is destroyed and loses its effectiveness. Water also turns cellulose (ground newspaper) to mush and it dries out VERY slowly (have you ever tried to dry out a wet newspaper?). The cellulose settles into a lump leaving a large un-insulated cavity in the wall. Of course, if it remains wet long enough, it can cause wood to rot and foster mold or mildew growth within your walls.