So, what’s the difference?
90% closed cell polyurethane foam, R value of 6.8
The easiest way to think of foam is to think of it liked whipped cream in a can. Two components involved: the cream and air.
If you increased the amount of air in the product by 10x, you would get a lot more coverage, but it would be a lot less dense. And since air is free, you’re paying less per ounce.
If you decreased the amount of air by 10x, you could cover less space, but it would be denser. And since there’s less air, you’re paying more per ounce.
With foam, the denser the product, the less water it can absorb.
Open cell foam is cheap, it expands more than a hundred times the liquid volume, it has a lower R-value, and it absorbs water readily.
Closed cell foam is more expensive, it expands about 30 times the liquid volume, it has a higher R-value, and it doesn’t absorb water readily.