Brush Seals and Pile Weatherstrip: Sizes, Types and Replacement for Retractable Screens

Pile weatherstrip (also called brush seal or wool pile) is a strip of dense fibers on a slotted backing that slides into a T-slot in a track, housing or bar. On retractable screens it closes the gap around the mesh edge, the housing slot and the bottom bar so insects cannot squeeze through. To replace it, measure the backing width, backing thickness and pile height, then match the type (plain or finned). This guide covers those measurements, the common sizes, and how to tell when it is worn out.

Where brush seals are used on screens and awnings

On a typical retractable screen, pile appears in four places:

• Side tracks: one or two strips per track, facing the mesh, keep it centered and close the edge gap. See screen tracks and guide rails.
• Housing slot: where the mesh exits the cassette. Pile here blocks insects entering the housing and wipes the mesh lightly as it retracts.
• Handle or bottom bar: a sweep on the bottom bar of vertical screens, or on the leading edge of horizontal door screens where the bar meets the latch jamb.
• Meeting stiles: on double screen doors that meet in the middle, pile on one or both bars closes the center gap; details in magnetic closures and latches.

Awning cassettes use similar brush or rubber strips where the front bar closes against the cassette, to keep wasps, debris and some water out of the rolled fabric. On cassette awnings a missing strip often means wasp nests inside the housing by midsummer.

Anatomy of pile weatherstrip

Pile weatherstrip is made of polypropylene (sometimes nylon or wool blends in older products) fibers locked into a flat backing strip. The backing slides into a T-shaped slot in the extrusion. Better grades are siliconized, which repels water and keeps the fibers from matting. Finned pile adds a thin polypropylene film down the center of the pile, which acts like a blade seal: it stops air movement and light much more effectively while the fibers protect and support it.

Plain vs finned pile

How to measure pile weatherstrip

1. Remove a sample. Slide a strip out of the end of the slot, or pull out a short piece. Measure an area that has not been crushed.
2. Backing width. Measure across the flat backing with calipers. This must match the slot; too narrow and it falls out, too wide and it will not slide in.
3. Backing thickness. Usually around 0.030-0.040 in (0.8-1.0 mm). Thick backing in a thin slot will jam.
4. Pile height. Measure from the top of the backing to the tips of the fibers, excluding the backing. Brush up the pile with a fingernail first; matted pile measures short.
5. Check the gap it closes. With the screen installed, measure the gap from the slot base to the surface the pile should touch. Pile height should be that gap plus about 1/32-1/16 in (1-1.5 mm) of compression.
6. Note fin and color. Fin or no fin, and color (gray, black, white, bronze are common).

Common pile weatherstrip sizes

European systems often specify pile in millimeters directly, such as 4.8 x 6 mm (backing x pile) or 6.7 x 10 mm. The first number is backing width, the second pile height; confirm the convention with the supplier because some catalogs list it the other way round.

Signs pile needs replacing

• Pile is flattened and does not spring back after brushing up
• Visible daylight through the track or meeting stile when the screen is closed
• Insects found on the inside of a closed screen, especially at night near lights
• Pile matted with dirt or pollen that will not wash out
• Backing has shrunk and pulled away from the slot ends, leaving gaps at the top or bottom
• Fins are torn or folded over

Typical life is several years, shorter at the bottom of tracks and on sweeps that drag over a sill. Component life expectations for screens and awnings are summarized in lifespan and maintenance data.

How to replace pile in a track or bar

1. Remove the end cap or bar. Pile usually slides out the end of the slot. On some tracks the top cap or bottom end piece must come off first.
2. Pull out the old strip. If it tears, use needle-nose pliers and a pick. Clean the slot with a vacuum and a damp cloth.
3. Cut the new strip slightly long. Add about 1/4 in (6 mm) to allow for shrink; polypropylene backing contracts slightly in cold.
4. Slide it in. A drop of dish soap on the backing helps on long runs. Do not stretch the strip as you feed it, or it will shrink back and leave a gap.
5. Crimp the ends. Pinch the slot lips lightly at each end with pliers, or use a dab of adhesive, so the strip cannot walk.
6. Test. Cycle the screen and check that it still retracts fully and that there is no daylight at the edges.

Brush seals vs rubber and bulb seals

Rubber or vinyl bulb and blade seals seal better against water and air but have more friction and do not tolerate moving mesh. They belong where two rigid parts close against each other, such as a front bar closing on an awning cassette or a screen bottom bar sitting on a level sill. Pile belongs anywhere one surface slides past another, which on a retractable screen is almost everywhere.

Frequently asked questions