Density is the whole game
Two PU squishies can look identical and differ 30 percent in weight. The heavier one is denser, rebounds slower and lasts longer on a keychain. Ask for the weight of every SKU — a supplier that cannot give it has not measured it.
Skin coating
A thin painted skin over open-cell foam cracks within weeks. Closed-cell foam with a bonded skin coating survives classroom use. Ask which it is; the price difference is small, the return rate difference is large.
Rise time
3–6 seconds is the standard slow-rise range for PU. Faster than 3 seconds reads as a cheap stress ball; slower than 8 seconds reads as broken.
Print quality
Airbrushed shading is what makes a PU banana look like a banana. Ask for a photo of the paint station, not just the finished piece.
Compliance
PU foam needs the flammability and heavy-metals sections of ASTM F963-23 and the CPSIA phthalate screen. Report numbers should be on the quote.
Source: U.S. CPSC recall notices of 3 Sept 2026 and 16 CFR 1250.4 (Federal Register, 12 Dec 2025).