Foam Raw Materials: what Claude and GPT would buy

Two AI models chose on their own, with no web access. Nobody tested these products: this is what each one says, and how to check it.

They disagree: Claude chooses FoamTouch and GPT chooses Smooth-On

In Industrial & Scientific, Claude and GPT choose the same brand in 52 of 107 categories.

Claude Opus 5.5 · October 28, 2026

FoamTouch (brand)

FoamTouch is a widely available upholstery-foam brand cut to common cushion sizes, with stated density and firmness options.

Not for: Cosplay or craft builders who need thin, carvable EVA sheets rather than polyurethane cushion foam.

GPT 6.1 Sol · November 10, 2026

Smooth-On FlexFoam-iT! III

Lightweight, flexible pour foam for custom cushioning, props, and prototypes; expands to fill molds and irregular spaces.

Not for: Structural loads, food contact, or projects without ventilation and protective equipment.

TNT Cosplay Supply (brand)

This brand specializes in high-density EVA foam that carves, heat-forms and seals cleanly for armor and props.

Not for: People looking for seat cushion or mattress foam.

Foam type. Use polyurethane or HR foam for seating, EVA for cosplay and floor pads, polyethylene for packaging and case inserts, and closed-cell foam for anything that gets wet. Each foam chemistry is built for a different job and fails quickly outside it.
Density (polyurethane). For seat cushions in regular use, look for at least 1.8 lb/ft³. HR foam is around 2.5 lb/ft³ and above for long-life seating. Density, not firmness, predicts how long the foam keeps its shape.
Firmness (ILD/IFD). Choose firmness separately from density. Lower ILD feels softer for backs; higher ILD is firmer for seats. Two foams of the same density can feel completely different.
EVA density. High-density EVA is best for armor, because it carves and sands cleanly. Low-density anti-fatigue mats tear and pit when shaped. Floor-mat EVA is cheaper but frustrating for detailed props.
Fire and indoor use. For furniture, check that the foam is stated to meet your local upholstery flammability requirement. Prefer CertiPUR-US where it is claimed. Requirements vary by region, and untested foam can off-gas strongly.

Shops seen in search results on November 5, 2026. A shop missing here may sell it too. Nothing was checked by a person.

Is denser foam always firmer?

No. Density measures material per volume and predicts durability. Firmness is set separately by ILD/IFD.