I wouldn't recommend using anything less than the closed cell foam (pink or blue stuff) and definitely not in peanuts form. As long as the foam sheets are carefully cut to fully fill the voids inside the pontoons, you'll get the maximum flotation. Without actually knowing, I'd estimate that the space between the peanuts might be 40% of the volume inside the pontoon that could potentially fill with water. Same for noodles and plastic bottles. I expect that the pontoons are sized just adequately to do the job if no water enters them. And before someone suggests that the seal on the outside of the pontoons is sufficient, then why would there be a need for flotation material at all, except perhaps as HotTommy said for structural integrity. - Grandad