Cheese Squishy 
Jellyfish Squishy 
Jumbo Lips Squishy 
Mummy Squishy 
Pop-Eye Rhino 
Salted Butter Stick 
Pink Lychee 
What is a foam stress ball made of?
A foam stress ball is a squeeze toy made from a soft, air-filled foam that squashes under your fingers and then recovers its shape. When a seller names the foam, the usual answer is PU foam, short for polyurethane foam. That is also why an old stress foam ball can go hard, split or shed crumbs: polyurethane foam ages, and the signs are well documented.
This page covers what that ageing looks like, what our own listings actually say about the filling, how a foam toy differs from a gel one, and what you can do at home to slow the process down.
Why PU foam cracks and crumbles as it ages
Museums that keep plastic objects deal with this problem on purpose, so their guidance is a good place to start. The Museum of Design in Plastics puts it plainly in its preservation notes on polyurethane: “Polyurethane foam is the most sensitive to environmental factors due to its increased surface area. Over time, exposure to oxygen and subsequent oxidation causes the foam to harden, crack and crumble.”
Two things follow from that sentence for anyone holding a PU foam stress ball:
- Foam is more exposed than solid plastic. A foam is mostly tiny cells, so there is a lot of surface for air to reach. That surface area is the museum’s stated reason foam is the most sensitive form of polyurethane.
- The change is gradual, not sudden. The museum describes it as happening “over time”, and hardening is one of the three signs it names. A foam toy that feels stiffer than it used to is worth watching.
The same source lists light, temperature and humidity as the factors polyurethane is “particularly sensitive” to. It does not give a lifespan for a toy, and neither do we: how fast a particular stress ball changes depends on the foam and on how it is kept.
What our listings say about the filling
We checked every active listing in our catalog on September 30, 2026 to see how often the material is actually stated. The answer is: not often.
| What the listing text says | Active listings |
|---|---|
| Mentions “foam” anywhere | 226 |
| Names PU (polyurethane) as the material | 10 |
| Names memory foam as the material | 4 |
| Total active listings checked | 1,076 |
So most foam squishies in our catalog, like most online, do not tell you which foam they use. The ten that do include the PU Foam Butter Squishy, the Cheese Squishy Block, whose listing says it is “molded from soft PU foam”, and the Jumbo Banana Squishy, a 7-inch PU foam piece. The Slow Rising Mushroom Squishy 2-Pack is one of the four that say memory foam.
If you want a polyurethane foam stress ball specifically, look for the material in the listing text rather than the photo. A photo cannot show you what the toy is made of.
Foam or gel: how to tell from the listing
Not every squishy is foam. In our catalog, 116 active listings use the word “gel”, and the way they describe the squeeze is different.
- Foam listings talk about rising back over time. The Cheese Squishy Block listing says “press it flat and it puffs back over several seconds”.
- Gel listings talk about denting and glitter moving inside. The Crystal Apple Squishy has “glitter shifting through the gel” and “dimples, then rises back slow”; the Jellyfish Squishy “dents, then comes back”.
The ageing described above is about polyurethane foam. We have no ageing data for our gel toys, so we are not going to claim they last longer or shorter; they are simply a different material with a different feel. If the difference you care about is how quickly a toy recovers, our guide to slow-rise vs fast-rise squishies covers that separately.
Slowing it down at home
A museum stores polyurethane in a dark, ventilated space, at 18 to 20 °C and 45 to 65% relative humidity, in a box that keeps dust off (again per the MoDiP notes). Nobody keeps a desk toy like that, but the same ideas scale down:
- Keep it out of direct sun. A windowsill or a car dashboard is the worst spot for a PU foam stress ball.
- Keep it away from heat. Radiators, heaters and hot cars all count. Heat damage is also excluded from our returns policy, so this one protects the toy and your options.
- Store it somewhere dark when you are not using it. A drawer or a box does the job.
- Skip harsh cleaners. Our policy excludes damage from harsh chemicals.
None of this stops ageing. It only avoids speeding it up.
When a crack is a return, and when it is age
Our returns and refunds policy (last updated September 22, 2026) gives you 30 days from delivery to request a return, refund or eligible replacement, and orders that arrive damaged, incorrect or incomplete remain eligible for a replacement or refund. If a foam toy arrives split, send your order number, a description and clear photos of the parcel and the product.
The policy does not cover items damaged through misuse, chewing, cutting, heat or harsh chemicals. A foam stress ball that slowly hardens and crumbles over many months of use and air is the material ageing, which is what the museum notes describe, not a delivery fault.
FAQ
What foam is used for stress balls?
Where our listings name it, the foam is PU (polyurethane) foam or memory foam. Most listings, ours included, do not name the foam at all, so check the listing text before assuming.
Why is my foam stress ball cracking?
Polyurethane foam reacts with oxygen over time, which makes it harden, crack and crumble. Light and heat make it worse, so a stress foam ball kept in the sun or near a heater will usually show it sooner.
Is a PU foam stress ball the same as a gel squishy?
No. A PU foam stress ball is an air-filled foam that rises back after a squeeze. Gel squishies are described in our listings as denting and coming back, often with glitter moving inside. They are different materials with a different feel, and the foam ageing described above applies to the foam one.
