Do mattresses have fiberglass?

Yes, many mattresses contain fiberglass, most often as a fire-barrier layer sewn beneath the outer cover. Not every mattress uses it, since some brands choose wool, rayon or other flame-resistant materials instead.

Fiberglass stays safely contained as long as a mattress cover is left on and zipped shut. Problems start when a cover is removed or torn, because glass fibers can escape into bedding and air. Foam and hybrid mattresses are the types buyers most often ask about, and a listing's materials section is the first place to check.

A fiberglass fire barrier sits under the outer cover, not in the foam comfort layers of a mattress.
CertiPUR-US certification tests flexible polyurethane foam only, so it does not address fiberglass in a mattress fire barrier.
CertiPUR-US caps total VOC emissions from mattress foam at 0.5 ppm, a separate concern from fiberglass.
Wool, rayon and other flame-resistant fabrics are the common non-fiberglass fire barriers in mattress construction.