Nasty chemicals are often the easiest way for manufacturers to create a flexible, mold- and noise-resistant insulator. For the planet's health, avoid toxic chemicals and minimize volatile organic compounds. For your health, look for formaldehyde-free, antimicrobial and hypoallergenic materials. Don't assume a natural material, such as wool or wood, is pure. It may be chemically enhanced to prevent mold and moisture. On the other hand, some synthetic rubber and polyurethane products may be formulated with minimal VOCs, and could be safer for allergy sufferers.