Cheap Sign Foam Alternative

[Jonathan]

go to diy store and get some polyeurathane foam for house insulation

I was going to suggest that. Two part polyurethane foam is good as you can just make a box the right size, work out the mass to mix to get the right density and fill it up. You do have to be quick, otherwise this happens:



You can get it in decent quantities here:

http://www.ecfibreglasssupplies.co.u...hane-foam.aspx

I keep meaning to get some myself for prototyping.