When you're shopping for a new mattress you're going to want one that can help you sleep soundly, and for many people that means having a mattress that doesn't contain any potentially harmful materials such as fiberglass.
A surprising number of even the best mattresses contain fiberglass, because it's a cost-effective flame retardant, and while it's no real danger when it's properly sealed, but if it somehow gets out, direct contact or inhalation can cause irritation and breathing problems.
