Short answer. “Foam weatherstrip” is not a complete material or replacement specification. Schlegel describes Q-LON as a layered family: a polyurethane (PU) foam core, polyethylene (PE) facing and—depending on the product—a reinforcing insert/backing form [F01]. Its QL 3097 page specifically names a polypropylene carrier alongside PE and PU [F02]. That does not mean the same carrier is present in every vintage, colour or mounting variation. Start by noting which layer or attachment is damaged rather than ordering by the appearance of its outer bulb.
The three separate identification questions
| Visible component | Published manufacturer role | Useful field evidence |
|---|---|---|
| Smooth, patterned or embossed outer skin | Q-LON range describes a PE film enclosing the foam [F01] | Photograph cracking, lifting, abrasion or missing surface; note whether there is a continuous external film |
| Compressible body under the skin | PU foam core [F01] | Note collapse or uneven contact without pulling, slicing or chemical testing the foam |
| Foot, base, strip or carrier anchoring the body | May contain PP, polycarbonate or fibre-cord reinforcement across the range [F01]; QL 3097 specifies a PP carrier [F02] | Record mounting edge, retainer channel, insertion direction, and any intact maker marking |
The groove is a feature of the window or door frame. The insert or carrier is part of a particular manufactured seal. Confusing the two causes a predictable purchasing mistake: a nearly identical PU dome can conceal a different foot, and the correct-looking colour may have no bearing on what the existing groove retains. Schlegel publishes multiple colours for the QL 3097 SKU [F16], which underscores why colour should be photographed but never treated as a code.
A useful close-up photo set
Take four photographs: (1) the whole opening with the seal’s position marked; (2) the seal contact surface viewed along the edge; (3) the attachment/groove with the profile still undisturbed; (4) an existing loose original sample against a ruler only if one is already safely available. Add a sketch showing which direction the sash closes, the visible base width and retention form; mark dimensions unavailable from an in-place photograph as not measured. Store imperial and metric measurements separately with unit labels.
Distinguish three possible problems
Film problem: a slit, detached film flap or coating on the facing may be visible even if the foam body looks full. That is a visual observation only: it does not prove water tightness, oxidation, chemical attack or which solvent is safe.
Foam/body problem: a compressed, collapsed or uneven body may appear; avoid manufacturing a “nominal” height from a measured used seal. For published recovery classifications and what they do not tell you about service condition, use the separate ageing identification guide.
Attachment problem: a torn carrier or damaged groove can create movement even if the weather-contact surface looks intact. Do not glue a loose unknown seal into a channel or machine out the receiver to accept a similar new part.
Can an ordinary rubber or EPDM D-seal replace this?
Not on the evidence above. The names “rubber,” “EPDM,” “PU foam,” “PE film” and “PP carrier” refer to different material/property questions; none alone validates shape, movement, mounting or compression range. An adhesive-backed strip and a kerf-retained Q-LON profile also represent different attachment systems even if both are offered for the same frame material [F17]. This is a no-confirmed-fit decision, not a claim that a properly engineered alternative can never exist.
If a manufacturer or installer identifies a documented replacement, keep the exact part number, system, production version, cross-section drawing and installation approval together. Without this, label the product merely a visually similar candidate. On smoke/fire-rated, egress-critical or warranty-sensitive assemblies, obtain the assembly manufacturer's instructions and competent professional approval before any change.
Manufacturer questions
Ask: What is the full part number of the seal pictured? What insert/carrier material and profile drawing apply to my generation and market? Was the original supplied as kerf-in, surface-fit or bonded? Does a documented replacement preserve the receiver geometry and operating clearances? Are any surfaces or finishes incompatible? Request a written drawing or service-bulletin locator rather than treating a brand logo as proof.
Original evidence and scope
- [F01] Schlegel, Q-LON seals, undated online range page,
Materials & Colours > Film/Foam/Insert: https://www.schlegel.com/products/qlon-seals/ (accessed 2026-10-12). - [F02] Schlegel, QL 3097, undated online SKU page,
Product features; material FAQ: https://www.schlegel.com/products/seal-technical-data-sheets/q-lon-3097/ (accessed 2026-10-12). - [F16] Same QL 3097 official page,
Colour Options. Colours not used for fit. - [F17] Schlegel, Products,
Seal selection by application > Q-LON fitment: https://www.schlegel.com/products/ (accessed 2026-10-12).
Boundaries: Original manufacturer pages establish range/SKU descriptions, not the chemistry of a reader's unmarked old gasket, the fitness of an EPDM replacement or a permitted modification. Related existing site: /profiles/kerf-in-foam-clad-compression/ and /brand-systems/schlegel-aquamac-qlon-code-reference/ (both dated 2026-10-10, read-only).