What is memory foam made of?

Memory foam is viscoelastic polyurethane foam — a polymer that flows slowly and springs back gradually. It is not natural latex. Density (kg/m³) and hardness (ILD/IFD) describe grade more precisely than the word memory alone.

Why does memory foam feel firmer in a cold bedroom?

Memory foam softens as temperature rises. Body heat creates a more moulding contact zone. Cooler room conditions leave the foam stiffer until it warms. That is a material property, not a defect.

Can you wash a memory foam mattress with lots of water?

No. Soaking memory foam traps liquid inside and dries slowly. That risks odour and material breakdown. Use low-moisture spot cleaning and a washable protector. See BedGuide's cleaning guide for foam-safe methods.

mattresses

Memory Foam Mattress Materials Science

Entity: memory foam mattress

Neat mattress with turned-down sheets on an upholstered bed in soft daylight — How a finished mattress and bedding stack can look once the bed is made.

In short

Memory foam is a type of polyurethane foam that slowly springs back after you press it. It also gets softer or firmer with temperature. Body heat softens the contact zone. A cooler room makes it feel firmer. Density in kg/m³ and indentation load deflection (ILD) describe the foam grade better than marketing thickness alone.

Cross-section diagram of memory foam layers showing viscoelastic comfort foam over denser support foam under pressure — Memory foam contours under heat and pressure; support foam beneath limits hammocking of the sleep surface.

Materials used

viscoelastic polyurethane foam
support foam base layers
cover textiles

Average lifespan

6– 8 years

How memory foam behaves

Memory foam (viscoelastic polyurethane) squashes under load and returns slowly when the load is removed. That slow return is what people feel as a “moulding” sensation. Pressure relief comes from spreading contact force over a larger area as the foam yields. That helps when shoulders and hips need sink for side-sleeping alignment.

Heat softens many memory foams. The same mattress can feel firmer when cold and more plush after body warmth builds. That temperature sensitivity is part of the material, not a defect.

Density vs hardness

Metric	What it measures	Why it matters
Density (kg/m³)	Mass per volume	Often links to how long the foam lasts
ILD / IFD	Force to indent the foam	Describes soft vs firm feel

High-density foam can still be soft. Low-density foam can feel firm but may wear sooner. Thickness alone does not define either metric.

Open-cell and gel-modified foams

Open-cell foam has more tiny air paths inside. That can feel cooler than classic slow-melting memory foam. Gel additives change how heat and touch feel. They do not turn foam into a different material.

Where memory foam sits in a mattress

As a full foam core (specialty foam mattress)
As a comfort layer over support foam
As a comfort layer over pocket springs in a hybrid

Care rules for foam

Unlike spring units with large air gaps, foam cores dry slowly once soaked. Use a waterproof or tightly woven protector. Rotate end-to-end on the schedule in turning vs rotating. Follow cleaning memory foam for spot treatment only.

Frequently asked questions

What is memory foam made of?: Memory foam is viscoelastic polyurethane foam — a polymer that flows slowly and springs back gradually. It is not natural latex. Density (kg/m³) and hardness (ILD/IFD) describe grade more precisely than the word memory alone.
Why does memory foam feel firmer in a cold bedroom?: Memory foam softens as temperature rises. Body heat creates a more moulding contact zone. Cooler room conditions leave the foam stiffer until it warms. That is a material property, not a defect.
Can you wash a memory foam mattress with lots of water?: No. Soaking memory foam traps liquid inside and dries slowly. That risks odour and material breakdown. Use low-moisture spot cleaning and a washable protector. See BedGuide's cleaning guide for foam-safe methods.