Polyester (PET) Brush Filament: Properties and Uses

What PET is

PET is made from terephthalic acid (or dimethyl terephthalate) and ethylene glycol. It crystallises more slowly than PBT, and the degree of crystallinity strongly affects its density and stiffness. Drawn monofilament is oriented and partly crystalline, which gives it its springy, stiff feel. For food contact in the US it is covered by 21 CFR 177.1630 (polyethylene phthalate polymers).

Crystallinity explains much of the variation between PET filaments. Fully amorphous PET has a density of about 1.37 g/cm³, while the crystalline phase is about 1.455 g/cm³, so a filament's density and stiffness depend on how it was drawn and heat-set. Copolymer versions such as PETG, and grades modified with isophthalic acid, crystallise less and melt lower. This matters with recycled bottle flake, which can include such copolymers, and is one more reason to approve samples before production.

Key properties with real numbers

PET's high melting point is misleading on its own. Its glass transition sits around 67–81 °C, and above that the amorphous part of the filament softens. Like PBT, it is also sensitive to hydrolysis in hot water above about 60 °C. For brushes, that means PET is best for ambient-temperature work, not hot washing.

PET or PBT: choosing a polyester

In practice PET is chosen where stiffness and price matter, as in brooms, household brushes and paint brushes. PBT is chosen for wet floor-care and roller brushes, where its faster crystallisation and toughness help it hold up under constant deflection. Both share the same hot-water weakness, so neither replaces nylon for hot washing.

Where PET is used in brushes

• Household and janitorial brooms and household brushes, where PET gives a stiffer sweep than PP at moderate cost.
• Synthetic paint brushes. Tapered and flagged polyester filaments are used to hold and release paint.
• Strip brushes and general cleaning brushes where low water uptake and stiffness are wanted at a lower price than nylon.
• Filament made partly from recycled PET bottle flake, used in some broom ranges. Consistency depends on how well the recycled feedstock is controlled.

Pros and cons

• Pro: stiff and springy at room temperature, with low water uptake, so brooms sweep the same wet or dry.
• Pro: good resistance to oils, many solvents and weak acids.
• Pro: competitive cost, with recycled options available.
• Con: filament producer data shows lower long-term bend recovery than nylon, so bristles can take a set.
• Con: softens above its glass transition and hydrolyses in hot water, so it is not suited to hot washes or steam.
• Con: denser than PP, so more filament weight per brush.

How to specify PET filament

Write PET, not just polyester, and give diameter, cross-section (round, X-shaped, hollow or flagged), crimp, trim length and colour. If you will accept recycled content, say so and agree a sample-approval step, because recycled PET varies more from lot to lot. For brooms, give block size, hole pattern and handle thread. For paint brushes, give the tip finish (tapered or flagged) and ferrule size.

If you are not sure whether PET or PBT suits the job, describe the duty in your RFQ: wet or dry, temperature, chemicals and how long the brush stays under load.

Alternatives to PET

PBT is the polyester of choice for wet floor-care and roller brushes. Polypropylene is cheaper and lighter for wet sweeping and scrubbing. PA6 or PA66 gives better recovery and abrasion life for dry-duty brushes.

Frequently asked questions

Is PET the same as PBT in brushes?

No. Both are polyesters, but PET is denser, melts higher and is usually stiffer. PBT crystallises faster and is the more common choice for wet floor-care brushes. Always state which one you mean.

Is a PET broom better than a PP broom?

PET is usually stiffer and sweeps fine dust and heavier debris more firmly. PP is lighter, cheaper and better for wet sweeping. For outdoor and wet use, PP is often preferred.

Can PET bristles be used in hot water?

Avoid long exposure. PET softens above its glass transition at about 67–81 °C and hydrolyses in hot water above about 60 °C.

Are recycled PET brush filaments any good?

They can perform well in brooms and household brushes if the feedstock is controlled. Ask for a sample and check diameter consistency and colour before production.

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