Fiberglass is a composite material made of glass and reinforced plastic that is sometimes used in mattresses as a cheap flame retardant. It is commonly found in memory foam mattresses and mattress covers because it is malleable and durable, making it easy for manufacturers to work with. Fiberglass is woven into a layer inside the mattress, which is only visible if the mattress cover is removed. If the mattress were to catch fire, the fiberglass causes the mattress to melt instead of burst into flames, which slows the spread of the fire and prevents it from reaching combustible materials inside the mattress as quickly. However, fiberglass can be dangerous if it escapes from the mattress. Smaller shards of fiberglass can fray from the woven layer and leak out of the mattress or poke through the cover, causing skin or eye irritation, allergies, and hazardous inhalation. Therefore, it is important to check the label on your mattress to see if it contains fiberglass.