Pile weatherstrip questions, answered

A dense bed of polypropylene filament anchored along a thin rigid backing. The backing seats in a slot in the window or door frame; the filament bridges the gap to the moving sash and seals it while still letting the sash slide.

Wool pile is the older trade name and it has outlived the material — on our lines the filament is polypropylene, not wool. Weatherpile, pile weatherstripping and fuzzy weatherstrip all describe the same part. On our lines the pile is heat-fused to the backing, polypropylene to polypropylene, with no adhesive in the bond.

The kerf is the slot cut into the frame or sash that the backing seats in. A kerf pile weatherstrip is pile weatherstrip with a flat backing sized to that slot — no adhesive, no fasteners. It slides in, and it pulls out again when it is time to replace it.

That is most of what we make. The backing width is the dimension that has to match your kerf, and it is one of the two figures a quote turns on. See the twenty-four widths already on tooling.

Usually yes — the same construction under a different trade name. The garage door industry says brush seal; the window and door industry says pile weatherstrip or weatherpile. We make both under the same roof and they run on the same lines.

The one case where the words mean genuinely different things is our square-base line, where rigid strands are mixed into the soft filament on a 3 mm square base rather than a flat backing. Diamond base and square base both describe that family.

A fin seal is pile weatherstrip with a polypropylene film running down the centre of the filament, standing slightly above it. Plain pile stops dust, water and rattle. It does not stop air: a filament bed is porous by construction, no matter how dense the pile is.

If your specification calls out an air-infiltration figure rather than just a dust or rattle requirement, the fin is the part doing that work. Silicone treatment is an option on the same strip rather than a separate product — outdoors, ask for both.

A sash that sits closed for a whole season compresses the pile the entire time. Filament that has not been heat-set takes a permanent bend, and a seal that passed inspection on day one has a gap by the second year.

Heat-setting the filament is what buys that height back. If you are replacing strip because of complaints about a flattened seal, that is the line to ask for.

On anything exposed to rain. Untreated polypropylene pile moves water by capillary action: on an exterior sash that means rain travels along the filament, past the seal and into the slot — the seal looks intact and the frame still gets wet.

Silicone treatment breaks that capillary path. Indoors, or on a sash under a deep overhang, it is not doing much.

Kerf-mounted if the frame has a slot — it is the stronger fixing and the cheaper part. Self-adhesive is for retrofit work, which almost never has a slot to slide into.

Between our two adhesive systems: foam tape takes up small steps and waviness in an existing frame that a thin adhesive film would bridge instead of sticking to, and it is the cheaper of the two. Acrylic transfer tape has no foam to shear under load and a lower total build height, so on a surface that is already flat, and for a bond meant to last, it holds better.

Two: backing width and pile height. Those are the figures a quote turns on. Everything else — fin or no fin, silicone or not, colour, spool length — changes the price but not the tooling.

If you also send 50 mm or more of the extrusion itself, we match the backing to the section rather than to a dimension on paper, which is more accurate. There is no charge for the sample or the tooling.

Any backing width you run, we make. The only thing that changes is how long it takes: twenty-four widths are on tooling now and sample in fifteen days, and anything else we cut a die for — fifteen days more, at our cost, not yours.

Where an existing die lands near a U.S. nominal rather than exactly on it, we publish the gap rather than round it away. Our standard widths are manufactured in millimetres, and you would find the difference on the first assembly regardless. A gap you can live with saves you fifteen days; a gap you cannot is what the dedicated die is for.

300–1,000 ft (91–305 m) is routine on standard sections. Wide backings and tall pile run shorter, so tell us the section along with the length you want and we will confirm before you order rather than after.