Expanding foam instead of air bag?

Newbie here…just reading about air bags and bulkheads to help keep water out of kayak…Why not use expanding foam (the kind that comes in a can for use as insulating foam) in the front and back of the kayak?? It’s light and easy to apply…

Very bad idea

why bad idea, please
Why is this not the same as an air bag…foam is very light and will keep some of the water out in case of overturning…

don’t use expanding foam as it may
expand to the point of deforming your hull. If you are going to do it I’d first mount a long bolt through the deck backed up with a washer and a nut on the inside in the area you will ‘foam’ for the foam to attach around so the foam wont fall out after hardening. And use the non-expanding foam, which expands only to the point of contact. I can’t imagine why there would be any issue with that at all, except the stuff may not be real durable over time.


– Last Updated: Jan-31-09 8:50 PM EST –

Huge volumes of it won't cure: It needs moisture from the air to cure. When you spray way too much into your boat the outside will cure and prevent the inside from curing. It will be a big sticky mess for a long, long time.

It is expensive: The get the same volume as an air bag will cost as much or more.

It is heavy: Not like lead, but certainly more than air.

It won't come out easily: What if you want to use that space for storage in the future?

It's not closed cell: It will hold water and things will grow in it.

Critters like it: Mice, moles, voles, chipmunks and squirrels like to tear it up and make nests in or from it.


Here’s a little story
I was given a canoe a while back. I did some outfitting on it, repaired the worst parts, and proceeded to wear it out some.

It was real heavy, and so I built a trailer for it.

It got rear-ended on the trailer, which knocked loose the rear bulkhead. In my preps to repair it, I removed the rear “flotation” from the bulk-head. In a previous repair, someone had used spray foam insulation instead of a proper flotation like closed cell extruded foam or styrofoam. It weighed about 40lbs and was dripping water two days after having last been in the river.

As soon as the skin is breached on cured spray foam (which will happen quickly with the flexing that happens in a canoe), that spray foam will turn into an enormous sponge, which is not useful for something that’s supposed to be there instead of water.

  • Big D

I heard something similar
Years ago my dad bought a little catamaran sailboat. He’d never done anything like that before so didn’t think much about the weight at first, but just built a trailer for it that was plenty heavy-duty. After not too long, he figured out that the boat weighed three times as much as it was supposed to, due to saturated foam in the two hulls. He made some access holes and dug out all the old foam, and re-filled it with new, then sealed it up again. About a year later he sold it, so I don’t know how the new foam held up, but it wasn’t the spray kind, but the two-ingredient mix kind.

It’s worth noting that normal boats use compressed polystyrene beads (the “fragile” and “cheap” kind of styrofoam) as floatation, and never a foam that cures in-place.

here’s another tip
You can get air bags which serve double-duty as dry-storage bags. It would be much better to go that route and have usable space where your floatation is.

In repairing my canoe
I intend to fill the space in the bulkheads by cutting kid’s pool noodles to the right length and cramming them in there. I can get pool noodles at dollar stores for cheap. They’re closed cell foam, will never absorb water, and they’ll take up space for a whole lot less than using an air bag. If it’s a sealed bulkhead where the flotation is going, I would recommend something along those lines rather than an air bag for thrift’s sake. However, if it’s in the main body of the boat rather than in a sealed off area, then the bags make a lot of sense - either storage bags or the regular kind of flotation bag.

  • Big D

I appreciate the education…thanks