PBT Brush Filament: Properties, Uses and How It Compares
Material guide · 6 min read · updated 2026-10-24
PBT (polybutylene terephthalate) is a polyester filament that sits between nylon and polypropylene. It barely absorbs water, so its stiffness hardly changes when wet, yet it is stiffer and more heat-resistant than PP.
That makes it a common choice for floor-care brushes, pad drivers and wet roller brushes, and a cost alternative to PA612 in many wet applications.
What PBT is
PBT is a semi-crystalline thermoplastic polyester made from terephthalic acid (or its ester) and 1,4-butanediol. It is a close relative of PET, but its longer four-carbon segment lets it crystallise quickly, which helps it hold a set shape after extrusion. In US regulations it is called poly(tetramethylene terephthalate) and is covered by 21 CFR 177.1660 for food-contact uses.
Filament quality starts with how the resin is handled. Polyesters are sensitive to moisture in the melt, and one resin producer specifies a moisture content below 0.04 % at processing, which means pre-drying the pellets. The same producer states that PBT melts are stable up to about 280 °C. Poorly dried or overheated resin breaks down during extrusion and gives a weaker filament that can turn brittle in service. When qualifying a new supplier, it is reasonable to ask how they dry the resin and to bend-test a sample of filament.
Key properties with real numbers
The modulus line shows why PBT works in wet duty. Dry PA66 is stiffer, but once the nylon takes up moisture PBT ends up well ahead, and PBT stays at roughly the same stiffness whether it is wet or dry. The density line shows the cost side: PBT is about 15 % heavier per unit volume than nylon, so the same brush volume takes more kilograms of filament.
| Property | PBT | PA66 |
|---|---|---|
| Melting temperature (DSC) | 223 °C | 260 °C |
| Density | 1.30 g/cm³ | 1.13 g/cm³ |
| Water absorption, saturated at 23 °C | 0.4 % | 8–9 % |
| Moisture at 23 °C / 50 % RH | 0.25 % | 2.5–3.1 % |
| Tensile modulus | 2,500 MPa | 3,000 MPa dry / 1,100 MPa conditioned |
PBT against other wet-duty filaments
Among the wet-duty options, PBT has the highest melting point and is stiffer than PP, but it is also the heaviest. PA612 costs more but recovers better from repeated bending and is the usual food-contact nylon. PP is the cheapest and lightest but softens at much lower temperatures. For many floor-care and wash-down brushes, PBT is the middle option that keeps cost down without the heat and recovery limits of PP.
| Property | PBT | PA612 | PP homopolymer |
|---|---|---|---|
| Moisture at 50 % RH | 0.25 % | 1.3 % | < 0.01 % (24 h immersion) |
| Water uptake when saturated | 0.4 % | 3.0 % | < 0.01 % |
| Melting point | 223 °C | 208–216 °C | 160–165 °C |
| Density / specific gravity | 1.30 | 1.06–1.07 | 0.90–0.91 |
Where PBT is used in brushes
- Floor scrubber disc brushes and short-trim pad drivers, where filament runs wet with cleaning chemicals.
- Flocked and high-density roller brushes, alongside PP and nylon options.
- Wet process rollers in washing equipment where nylon would soften.
- Toothbrush, cosmetic and paint-brush filaments, where polyesters are chosen for consistent wet stiffness.
Pros and cons
- Pro: very low moisture uptake, so stiffness and cleaning action are consistent wet or dry.
- Pro: higher melting point and stiffness than polypropylene.
- Pro: good resistance to oils, fuels and many solvents.
- Con: polyesters, including PBT, are sensitive to hydrolysis in hot water above about 60 °C. For long exposure to hot washes, check grades with improved hydrolysis resistance or use PA612.
- Con: filament producers report that nylon has better long-term bend recovery than polyester, so PBT brushes can take a set sooner under constant deflection.
- Con: higher density than nylon or PP raises filament weight per brush.
How to specify PBT filament
Give polymer (PBT), diameter, crimped or level, trim length and colour, plus the working conditions: water temperature, cleaning chemicals and pH, and whether the brush sits under constant pressure. For pad drivers, give the machine model, pad size and mounting type. Our floor scrubber brushes list typical disc and driver formats.
If the brush will be used on food lines, say so in your RFQ. PBT's food-contact status depends on the resin and its additives, so a declaration of compliance is needed in the same way as for nylon.
Alternatives to PBT
For hotter wet service or better recovery, use PA612. For the lowest cost and lightest weight in cold-water scrubbing, use polypropylene. For brooms and paint brushes, PET polyester is another option. For aggressive floor stripping, an abrasive filament cuts much faster than any plain filament.
Frequently asked questions
- Is PBT better than nylon for brushes?
- In wet service, PBT keeps its stiffness much better than PA6 or PA66 because it absorbs only about 0.4 % water. Nylon recovers better from repeated bending and tolerates hot water better, so neither is better in every case.
- What is the melting point of PBT filament?
- A typical PBT resin melts at about 223 °C by DSC.
- Can PBT brushes be used in hot water?
- Short contact is fine, but polyesters such as PBT are sensitive to hydrolysis in hot water above about 60 °C. For long exposure to hot washes, choose hydrolysis-resistant grades or PA612.
- Why are pad drivers made with PBT bristles?
- Pad drivers run wet with cleaning chemicals under constant load. PBT keeps its stiffness when wet and is stiffer than PP, so it grips the pad consistently.
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