This is a cool idea, but I see a few problems. Applying it perfectly evenly would be just about impossible. As a result, the surface of the cushion would be lumpy and unattractive. I don't know if polyurethane foam will skin over without a mold, but even if it does, the skin will not be very durable. You don't see chairs with foam seats that are not covered with fabric or vinyl for this reason. Applying a premade foam pad to something with an appropriate adhesive is pretty easy anyway. I'm not sure if spraying the foam on would be any easier.

Dwane, I'm thinking of for instance coating the interior sidewalls of a kitplane or the back-seat area of a street drag-racing car where the seats have been removed for weight savings. it would be more specialized for an area where you don't have a panel or seat to 'cover'--you just spray it on and it would stick, form and skin. Actually, using a product with these properties would allow easy building of furniture out of 2x4's and plywood, too. Spray the walls of your kids' rumpus room and no-more bumped heads.

Traditional upholstery methods would seem really more difficult what with the purchasing, measuring and cutting and cloth and foam, the stapling or button-tucking, etc. I'm talking truely one-step covering--just spray and wait. Also, you could vary thickness at will by spraying more or less before it's dry. Lumpy? a matter of skill--like painting with a spray can. You could learn to keep it even.

I don't think polyurethane foam as it's made now would work for this, but yes, 'Great Stuff' is a urethane of a type and it does skin over, unfortunatly the whole quantity becomes rigid--something I can't have with this.

I have to believe there are or have been people working on an idea like this before my suggestion--it doesn't seem so far-fetched to me.

Yes, for applications where appearance isn't too critical, like the insides of kitplanes, race cars etc., this might work great. I think the unevenness problem would be harder to avoid than you think. The problem is that any slight variation in thickness will be amplified tremendously as it expands. You see this with Great Stuff. With Great Stuff, you can trim it easily with a knife after it hardens, but that's because it's rigid. It's very hard to trim flexible foam rubber evenly. I know because I've tried it.

Interesting idea.

Like Dwayne mentions, controlling lumps may be the biggest hurdle.

Also see http://www.fabricanltd.com/

interesting link painperdu. Note, NSFW.