What sort of white foam, and how strong does it need to be? L
it is a pure foam w 5 g/cm density and i want it very strong
What polymer / material is it? It matters for the adhesive, right glue for the job thing. L
It depends what you want to do with it. Does it need to be waterproof? If not, then a PVA craft glue or woodworking glue should work, but might not withstand too much moisture. 3M makes a spray on upholstery glue which is good for foam. If you need something very strong I have heard that a two part epoxy glue will do the trick (never tried it). I have used contact cement to stick soft foam (sponge) together, so it may be OK for polystyrene. Make sure you test on a sample of your foam first as the foam may dissolve with the wrong glue.
thnx i tried it it is very god but it is very expensive
PVA glue (wood working glue) is about as cheap as glue gets. Buy it from a trade place in a BIG container to get a cheap deal.
Foam adhesive can be bought at any hardware store. It's specially designed not to melt the foam, as other glues may do. It's very effective at gluing ridid foam to just about anything!
Double sided or double stick tape might work if all you want is get the pieces together.
UHU POR is the best I've found. It's a contact adhesive (coat both surfaces, wait 5 mins then stick together) which is very strong and waterproof and safe for just about any foam. Any good model shop should sell it.