I use blue foam inside sailboards but... The weight of the foam has just increased by 36% the australian distributer has told me it's because they have changed the blowing agent and the weights of the foam are only the minimal weight,So I rorked out the blue foam is now about 39/m it's now a lot harder to shape as it's more dense. I am looking for another source of closed cell extruded polystyrene other than the dow chemicals blue foam. Does any one out there know of another manufacturer???? From experience and talking to other board manufactures glass over the foam will delaminate easily as the foam compresses in and stays compressed in, but the covering glass flexess back out to it's origional shape leaving a delamed area. I have made blue foam boards covered with 5 mm divinycell sandwhich that still look like new after 3 years of hard use by No 1 W.A. wavesailer in Greenhead.

a.k.a. KA202

I've also used the old blue foam, when I bought it it came in several densities I think the stuff I got was about 40Kg/M3.
As blue juice says, if you only use cloth on it it delams quite quickly.
The most comon D-cell density is 80kg/M3, 3mm of that with a layer of 200 gm/M2 cloth each side is about right for most of the board, under the feet area you could add the same weight carbon for good luck.
The guy who sold it to me, told me not to try bending it, as it's much stiffer than ordinary styrofoam.

If you can't source divynicell, try herex, actually I prefer it d-cell it sands a bit better.


decrepit

Hi Decrepit I have been using the IB which is stated as 28kg but the last block I bought with IB stamped on it was 39kg, This 28kg is the minimum weight it will ever be and not go below that. I was told the new blowing agent is more enviromentally friendly but causes an increase in the weight of the foam and that extra weight probably doesn't matter when its being used for its primary purpose of insulation, thanks for looking though
I dont think they make div very light.
I will find a new source!

a.k.a. KA202

decrepit my current board(experimental) is made from that ultra light stuff from Burford. I like to test them for a while It's 10 months old and seems to be holding up. The Burford foam has no where near the compression strength of the blue foam.
Crashtest d I've been thinking if I made a K board I'd buy a sheet of 8mm div or heirex cut out 3 plan shapes put a layer of 200gm glass and epoxy between 1st and 2nd sheet then again between 2nd and 3rd sheet Put this in a vac bag to stick em all together, place the bag ontop of a pre shaped rocker bed and weight it down while it all dries to shape in the bag, then pull it out and reshape the deck & rails, then put on the outside glass.

a.k.a. KA202

yep theyre about 30kg/m usually with that kind of blank the foam is usually denser near the skin and less towards the middle.

a.k.a. KA202