I have always questioned why a certain major "Swedish foam" mattress manufacturer would tell customers on their web-site that off-gassing is normal and all that you need to do is open the window and let it air out for a few hours once you bring it home.  I have had customers who asked for refunds because the issue with off-gases did not stop.  

One final issue that concerns us is that even premium quality luxury mattresses on the market today are almost entirely made from petrochemicals, in fact it takes a 55 gallon drum of these chemicals to make a queen size mattress.  This explains the off-gassing.  It also explains why mattresses made with synthetic foams are highly flammable and why the government passed a flammability law called FR1633. A law, however well intentioned, that has led to even more chemicals being poured into the manufacturing process of mattresses.  When caught on fire, fire fighters will tell you the toxic gases from the mattress which is Hydrogen Cyanide and carbon monoxide is as deadly as the mattress fire itself.