Polyester or polyether.
Two polyurethane chemistries that look identical and age completely differently. Which one your application needs depends mostly on how much moisture it will live with.
One bond, large consequences.
Both materials are polyurethane. What differs is the polyol used to make them, and with it the chemical backbone of the finished foam. You cannot tell them apart by eye or by touch — you find out which one you bought two years later.
Polyether has a backbone that water does not readily attack. It stays flexible and intact through years of humidity, which is why it is the standard for air filtration.
Polyester has ester linkages that water can break — hydrolysis. In warm, damp conditions the polymer gradually reverts, and a polyester foam that has hydrolysed goes sticky, then crumbles. In exchange, polyester can be made with finer and more uniform cells, and it takes a rougher strand surface that grips liquid well.
Which does what.
| Property | Polyether | Polyester |
|---|---|---|
| Humidity | Resistant — the reason it dominates air filtration | Vulnerable to hydrolysis in warm damp conditions |
| Cell fineness | Good across the normal range | Can be made finer and more uniform |
| Strand surface | Smooth, from thermal reticulation | Rough and etched if chemically reticulated — holds liquid |
| Reticulation route | Thermal only (zapping) | Thermal or chemical (quenching) |
| Best for | Air, gas, general filtration, anything outdoors | Liquid retention, wicking, fine-pore controlled environments |
The reticulation row explains something that otherwise looks arbitrary: because polyether cannot be chemically reticulated, some very fine grades are only practical in polyester. The chemistry and the process are linked rather than independent choices. See how reticulated foam is made.
Polyether, as standard.
We cut polyether foam, because the overwhelming majority of what we supply is air and gas filtration — and for that, polyether is not a compromise, it is the correct material. A polyester air filter in an Indian summer is a warranty claim waiting to happen.
If your application genuinely calls for polyester — sustained liquid retention, ink or fluid transfer, a fine-pore grade in a dry controlled environment — tell us what the part has to do. We would rather point you to a specialist supplier than sell you the wrong chemistry and have it fail in service.
Common questions.
What is the difference between polyester and polyether foam?
They are two different polyurethane chemistries, distinguished by the polyol used to make them. Polyether foam resists water and humidity well and is the standard choice for air filtration. Polyester foam can be made with finer, more uniform cells and takes a rougher strand surface that holds liquid better, but it is vulnerable to hydrolysis — breaking down in prolonged warm, damp conditions.
Which one should I use for air filtration?
Polyether, in almost every case. Air filters live in moving air of unpredictable humidity, and that is precisely the condition under which polyester degrades. Polyether will still be flexible and intact years later. The exception is a specialised fine-pore requirement where polyester's cell uniformity genuinely matters and the environment is dry and controlled.
Why is polyester used at all if it can hydrolyse?
Because in the right application its properties are better. The rougher, etched strand surface produced by chemical reticulation grips liquid by surface tension, which matters for wicking, ink transfer and fluid retention rather than for airflow. It also reticulates chemically, which polyether does not — so some very fine grades are only practical in polyester.
How do the two reticulate differently?
Polyether can only be reticulated thermally, by the zapping process — a controlled flame front through a sealed vessel. Polyester can be reticulated either thermally or chemically in a caustic bath. That chemical route is what gives the etched strand surface, so the chemistry and the reticulation method are linked rather than independent choices.
Which do you supply?
Polyether as standard, because the overwhelming majority of what we cut is air and gas filtration where polyether is the correct material. If your application genuinely needs polyester, tell us what it has to do and we will be straight about whether we can help or whether you need a specialist supplier.
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