If this is pink then it is probably not the kind of foam as you would want for a seat. It is most likely a polystyrene foam (the blue stuff is real Styrofoam (R) which would float, but is not as flexible or comfortable as the synthetic rubbers used in the closed cell foam for kayaks.

You can use it for flotation. You might get a better price on the full 4x8 sheets of similar material. I have seen those available in 2 inch thickness. Cutting those into large blocks would give you some significant flotation, and you would eliminate the folds.

You should be able to glue several layers of these materials together to make a larger block of flotation. Try using construction adhesives, like "Liquid Nails" which comes in a caulking tube. Check the label to see if they can be used with foam insulation. Some brands have solvents that dissolve the plastic.

This is nice cheap stuff to use to pad out areas in the cockpit to reduce the amount of water that can come in if you capsize.

Most of these foams do not have very good resistance to abrasion. Unless you cover it with something you'll get bits of plastic all over the place if you regularly rub against it. Try using a spray adhesive and stretching some Lycra or stretch-nylon swimsuit fabric over your foam construction. I think it was Spidey who used this technique with his minicell seat with good results.

Other people cover this material with fiberglass and epoxy resin (polyester resin will dissolve styrene plastics) You can use this technique to make buoys, rafts, surfboards and sit-on-top kayaks, too.

hope this helps

PGJ