When I was building my upholstered benches for the boutique I knew I wanted thick, dense foam for the cousions. The problem with that is I was going to resell the benches so I really needed to keep my costs down so I could make a profit. All of a sudden a light bulb clicked on in my head. Crib mattresses!
I happened to have two, all-foam, sealed in the plastic crib mattresses sitting in my guest room. I stripped the plastic and liners off and checked them out. It was perfect! 5 inches thick, super dense foam.
In actuality, it's not really foam. Its more like a really dense batting, which actually holds up better to use than foam. It's perfect for seat cushions.
I cut mine just like any other kind of foam, with an electric knife.
My knife is like 30 years old and smells weird when it turns on, but it works like a champ and cost me $4 from a thrift store.
*Another cool foam secret (this one taught to me from the husband): to smooth and shape foam, use angle grinder with a sanding disk on it.
* It's cheap. If you are doing a DIY project you can use a "Used" mattress you have laying around, or even one you find on craigslist. Most of them are sealed in a plastic wrapper, so totally hygenic. I've seen some listed on craigslist for as little as $5 before. If you are planning on reselling the item, or don't have a used mattress available, new foam crib mattresses are still WAY cheaper than 5 inch High Density Foam. Wal-mart sells this one for $39.
* It holds up REALLY well.
* Large enough for most projects.
* Limited size (Standard crib mattresses are 52in x 27.8in)
*Harder to cut
*It has to be ALL foam. Coils or springs wont work unless you are using the full sized mattress.
I've used crib mattresses for a few projects now, and have every plan on using them again