Identifying foam type

I recently found a load of offcuts of foam sheeting from a domestic construction site (Melbourne, Australia) and figured I’d take a departure from timber and have a go at this foam shaping malarky.

Can anyone offer any hints on identifying what type of foam it is? My quick research suggests that we use EPS and XPS (extruded polystyrene, or styrofoam) for housing insulation in Australia. I’ve never clapped eyes on the builder, so asking him isn’t likely.

Also, are there any likely looking foams that tend not to be suitable for shaping and glassing? I’ll be using epoxy and bamboo fabric if that makes any difference.

Cheers,

Mat

Im not too sure about this one, but maybe to narrow it down pour a drop of polyester resin on the foam. If the foam starts dissolving the the foam is made from polystyrene, thus only epoxy can be used to laminate a board made from this foam. If, however, the polyester resin does nothing to the foam than it could be poly-urethane foam. This type of foam can be laminated with both epoxy and poly resins. There are also various densities of the foam, however in think the only way to find out is to compare the foam you have to a foam of known density, match up the texture. Hope this helps. Not sure is same applies to XPS or EPS. But you can build boards out of PU, PE, XPS, EPS and other biofoam foams. Sorry if wrong, i’m a noob/kook myself, but thats what i’d do.

Hi Mr Retro

 

Thanks for your advice—it’s pretty sound to me. Whilst I don’t have any polyester resin, I think there is some in the varnish I use, and Gorilla glue. I’ll check on that, and see if they reveal any secrets.

 

I guess at the end of the day, I’m building with epoxy anyway, so it’s more for trivia’s sake that I’m trying to find out.

 

Cheers.

Please do not think I am being insulting, but to tell if it is extruded EPS (XEPS), suck on it.  Regular beaded will breath, and the extruded will be like sucking on lumber.  Well fused EPS can also be evaluated vs. another that way.  In SOCAL there is still a surplus of cheap EPS blanks.  Just PM.

 

Sickdog

Matt:
Some good advise there, but this should be pretty easy to
determine what you have. Even tho I’m not in your neck of the woods,
there are some basic rules that all construction foam follows.
EPS: this is formed from bead and when fused, still looks like bead.
Take your thumb to an edge and scrape. If beads flake off, you have EPS.
Also, you can take a piece and break off a corner. Look at the seperation.
If you see flat-sided beads, EPS again.
XPS: there is no bead here, foam is made from a polystyrene liquid. Looks
like tiny closed compartments. Fingernail scrape produces no beads. You
can suck it if u want… Break it and it looks like regular surfboard foam. If
it is pink or blue in color, for sure it’s XPS.
Density: all foams are rated on pounds per cubic foot here in the US. you might
find that foams there are rated in kg. per cu. meter… don’t know. How to tell
density? Well if you have any of the paper off the insulation sheets, go to the
manufactureres web-site. The math way is to cut a small 1" cube (or 1 cm cube),
weigh it on a gram scale, (you should know someone there with a scale, LOL)
and do the math to arrive a lbs/cu. foot. (hint: a cu.ft. is 12 x 12 x 12 inches)
Your foam however is probably under 1.5 lbs as heavier foam has less of an
insulation value and the cost vrs. value goes way down. Hope this helps!