What is a mattress made of?

Pocketed steel springs, or high-density polyurethane foam

Pocketed springs move independently so movement doesn't transfer across the bed. Foam cores are quieter and lighter but rely entirely on foam density for their lifespan.

Viscoelastic (memory) foam, latex, or gel-infused polyurethane

Viscoelastic foam softens with body heat and conforms slowly. Latex springs back immediately and sleeps cooler. Gel infusion adds thermal mass rather than actual cooling.

Medium-density polyurethane foam

It stops you sinking through the soft top onto the hard core. Cheap mattresses omit it, which is why they feel supportive briefly then bottom out.

Woven fibreglass, rayon-silica blend, or treated cellulose

Required to meet flammability standards. Fibreglass barriers are the reason removing a mattress cover is often explicitly warned against.

Knitted polyester, viscose, or cotton blend, quilted to a thin foam

The quilting adds the initial surface softness. Fibre choice affects how the surface handles moisture more than how it feels.

Reinforced foam rail or a higher-gauge perimeter spring

It stops the edge collapsing when sitting, and it's the first thing removed to cut cost — noticeable within a year on a bed used by two people.