PA66 (Nylon 6.6) Brush Filament: Properties and Uses
Material guide · 6 min read · updated 2026-10-24
PA66 (nylon 6.6) is the workhorse filament for industrial brushes. It has the highest melting point of the common brush nylons and, when dry, it is one of the stiffest, which is why it is often the default for roller brushes, strip seals and cleaning brushes that run on machines.
It still absorbs water, though less than PA6, and loses a large share of its stiffness when soaked. Knowing where that line falls is the key to deciding between PA66 and the more expensive PA612.
What PA66 is
Nylon 6.6 is made by condensing two six-carbon building blocks, hexamethylenediamine and adipic acid. The regular, symmetrical chain packs into a crystal structure that melts about 40 °C higher than nylon 6, which gives PA66 its better heat resistance and dry stiffness.
In brush making it is extruded as level or crimped monofilament, in round and sometimes shaped cross-sections, and is the base polymer for several speciality filaments, including some carbon-coated conductive nylons.
Key properties with real numbers
The last two rows explain most field complaints about PA66. A filament producer's bulletin, citing standard nylon data, notes that PA66 is very stiff when dry but loses about 65 % of its stiffness as humidity rises from 50 % to 100 %. At around 60 % relative humidity, PA66 and PA612 have about the same stiffness. Above that, PA612 is the stiffer filament.
| Property | PA66 | Compared with PA6 |
|---|---|---|
| Melting temperature (DSC) | 260 °C | About 40 °C higher (PA6 ≈ 220 °C) |
| Density | 1.13–1.14 g/cm³ | Essentially the same |
| Water absorption, saturated at 23 °C | 8–9 % | Slightly lower (PA6 9–10 %) |
| Moisture at 23 °C / 50 % RH | 2.5–3.1 % | Slightly lower |
| Tensile modulus, dry / conditioned | 3,000 / 1,100 MPa | Similar drop on conditioning |
| Filament modulus ratio, wet / dry | 0.35 | Larger relative drop than PA6 (0.50) |
| Short-cycle max service temperature (resin) | 200 °C | PA6 grade listed at 180 °C |
Where PA66 is used in brushes
- Solar panel cleaning rollers, which commonly use soft, fine PA66 filament. Its higher melting point than PA6 gives extra heat headroom for rooftop work.
- Conveyor cleaning brushes and cylinder brushes for dry or intermittently wet belts.
- Door, garage-door and weather seal brushes, often 0.3–0.4 mm filament in aluminium holders.
- Industrial strip brushes, spiral-wound rollers and disc brushes where dry stiffness and abrasion resistance matter.
- Base polymer for some conductive and anti-static nylon filaments.
Pros and cons
- Pro: highest melting point and best heat headroom of the common brush nylons.
- Pro: high dry stiffness and good abrasion resistance, so it holds cleaning action in dry service.
- Pro: resists fuels, lubricants and most chemicals, according to resin producer design data.
- Con: absorbs 8–9 % water at saturation, and its stiffness falls sharply when wet.
- Con: attacked by strong acids, phenols and oxidising agents.
- Con: costs more than PA6 and, for constantly wet duty, gives poorer value than PA612 or a polyester.
Heat, cold and ageing
PA66's main advantage over PA6 is heat. Its melting point is about 40 °C higher, and the resin datasheet gives a temperature index (50 % loss of tensile strength) of 118 °C after 5,000 hours and 101 °C after 20,000 hours. In the US food-contact regulation, the specified melting range for nylon 66 resins is 246–257 °C (475–495 °F), with specific gravity 1.14.
Long-term heat still matters. A filament producer's rule of thumb is that nylon degradation roughly doubles for every 5 °C rise, so a brush running at 80 °C ages far faster than one at 50 °C. Nylon also stiffens in the cold, to about twice its room-temperature stiffness at 0 °C, without becoming brittle. That makes PA66 a sound choice for outdoor seals and rollers that see both summer heat and winter frost.
Moisture also changes dimensions. Resin design data shows PA66 grows by about 0.6 % at 50 % RH and about 2.6 % when saturated. In a fine filament this is a small change, but in tightly packed strip seals it can affect fit and drag.
How to specify PA66 filament
State "PA66" explicitly rather than "nylon", along with diameter, crimped or level, trim length, colour, and any anti-UV or heat-stabilised requirement. For rollers, give the core or shaft dimensions and the duty: dry dust, rinse water, or continuous spray.
If the brush runs wet for most of its life, ask the factory to quote PA612 alongside PA66 so you can compare. For dry, warm or outdoor duty, PA66 is usually the better value. The solar panel filament guide covers one common PA66 application in more detail, and our nylon grades comparison puts the three grades side by side.
Alternatives to PA66
Use PA612 for wet, food or chemically harsh environments. Use PBT for wet scrubbing at lower cost than PA612. Use PA6 when the duty is dry and price is the main driver. Where the brush must also cut or deburr, look at silicon carbide abrasive nylon instead of plain filament. Send your duty details with an RFQ and we will quote the grades that fit.
Frequently asked questions
- What is the difference between PA66 and PA6 brush filament?
- PA66 melts at about 260 °C against about 220 °C for PA6, and it is stiffer when dry. Both absorb a lot of water. PA66 absorbs slightly less, but its stiffness drops by a larger proportion when wet.
- Is nylon 66 good for wet brushes?
- It works for intermittent wetting, but it loses much of its stiffness when saturated. For brushes that run wet all the time, PA612 or PBT keeps its cleaning action better.
- What temperature can a PA66 brush handle?
- The resin melts at about 260 °C, and one producer lists 200 °C for short-cycle exposure. Continuous brush service should stay far lower because stiffness drops as temperature rises and long heat exposure ages the polymer.
- Why are solar panel brushes made from nylon 66?
- Fine PA66 filament is soft enough for panel glass, and it has more heat headroom than PA6 for rooftop work. Most panel cleaning is dry or lightly wetted, where PA66 keeps its stiffness well.
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