From the article, quote is from the mattress manufacturer:
"Our mattresses are tested and certified by third-party laboratories and meet or exceed all regulatory and safety regulations. In order to meet U.S. federal mattress flammability standards, many memory foam mattresses are constructed with a fire retardant knit fabric barrier that includes glass fiber threads,” says Rick Leckner, who handles Corporate Communications for DHP Furniture.

Leckner’s email statement went on to say: “Glass fiber threads in the fire barrier is commonly used across the mattresses industry, and our fire barrier is concealed under the quilting of the mattress cover.”