Confor foam (used to be called Temperfoam), as son of flubber and Cindy suggest, is the stuff to use.

Available at http://www.cumulus-soaring.com/e-a-r.htm as well as other suppliers.

For maximum safety benefit, and comfort too, I recommend using the green (extra firm). Even though in cold weather it will be hard as a rock for a few minutes, it'll soften up and conform to your body in not time. Extremely comfortable over a long period as it evenly supports the body.

The extra firm absorbs more energy in compressive loading that does the less dense versions, though for thick, more cushy seating, as well as initial comfort, less dense foams like blue and pink are often layered together - - and that's fine, and what I have in my power plane, as long as there's plenty of room for a thicker cushion. In a glider that's not always or often the case, so you want to use the dense version to maximize the absorption over the minimal distance available to protect the spine.

Confor does not do UV or abrasion well, it must be covered to last. When making properly constructed seat cushions (i.e. not just wrapped in a pillow cover and thrown in a glider), it's often covered with a thin, 1/4" thick layer of cheap polyfoam before fitting the cover ,this allows the cover to fit better.

If building your own seats and needing to shape the foam, an old electric kitchen knife works well, a band saw is nice to have but you can do without it. If you have to sand it, it makes a helluva mess and you will end up looking like a green smurf. Glue and laminate using 3M 77 or 90 spray adhesive..

It's easy to glue layers to get thicker, and hard to cut a thick slab when you need thinner - a consideration when ordering.

bumper