I think nearly all of the soft plastic materials contains dubeous substances. Formaldehyde is one, even more common these days are bisphenol A and B, phthalates,... The list is probably long. Some of the odd smells are probably just a bit unpleasant, like the rubber inner tubes for bike tires. Some of these smells I'm convinced are due to solvent residues, very much like white spirit. The problem is we never get a full list of ingredients when it comes to this, it's just called PVC, plyurethane, polyester, butyl, leatherette... A part of this is dute production secrets too, the best hightech fiber treatments for water proofing, stain proofing, etc. It's too much info to put on the back side of a wash lable.