> If you poked a whole bunch of small holes (with a nail or something)
> in the soda bottles then would they crush and absorb the force of
> the expanding foam - thus preventing the foam from bursting your kayak?
>

> Alternatively, could you just blow up a couple of balloons and
> use them since they would easily be compressed by the foam?

> Pete

I don't know if that would work but the idea of using the bottles was not to absorbe expansion but to reduce the amount of foam used. You need to use this foam a couple of times to learn how much to inject into an area so as not to over fill it and you need a place for the foam to over flow if you use too much.