Some of those peanuts are cellulose and will dissolve in water.
"Barrett Bonden" wrote in message
news
Will Styrofoam take on water ? I refer to those ubiquitous small "peanuts"
used in packing and shipping ; I want to add some permanent floatation to
a
beat up old fiberglass dingy : I've one seat compartment opened now (I've
given up on sealing all the holes, now or future ) and it occurs to me
that
filling the interior of the seat with these things would be useful if they
didn't waterlog.