: This seat looks fantastic. I would like to make one.
: Having said all of that, my next question is about minicel foam.
: The product is not available in australia under that name. It is sold under
: the trade name "softlon" here and may be difficult to obtain in
: the correct thickness. Is there any reason why I should not use
: conventional P.E. closed cell foam in the same manner?

If you mean Ethafoam (from Dow) or similar expanded polyethylene foam, no, it's not a good substitute. The pore size is very large, so once you cut through the skin, you end up with a relatively rough surface that will hold a fair amount of water. It does not carve well with Surform tools or dragon skin. It also breaks down much faster than Minicel, unless you use one of the denser grades (4 or 6 pound/ft3) which are not flexible.

Minicel is made in "buns" which are ~ 4' square and a bit over 3" thick. If you cannot find the thick stuff, it's a simple matter to laminate thinner layers with contact cement to get the desired thickness.