Short answer. Andersen describes short foam weatherstrip at all four sash-frame corners of a 400 Series gliding window, within the bulb weatherstrip region. The short corner pieces are not the same object as a continuous rail/stile seal, nor the small frame head/sill plugs covered by a separate manufacturer article. Locate the missing material before searching for a long strip by its cross-section. [S:AND400CORNER] [S:ANDGLIDEAIR]
A corner-first location map
| Where the material appears to be missing | Candidate to investigate | Evidence you need |
|---|---|---|
| In a sash corner, between the ends of adjacent sash weatherstrip | 400 Series corner foam | Close-up showing rail, stile and existing foam junction |
| Along an extended edge of sash | Rail or stile weatherstrip | Entire edge plus cross-section, not only a 1-inch fragment |
| At the top or bottom of frame where sashes meet | Head or sill plug, not automatically corner foam | Wide view of frame junction; compare maker's plug article |
| Along middle meeting edge | Meeting-stile or check-rail type, depending on series | Whole-window series and operating/stationary sides |
Andersen's corner-foam support page describes an interface between the hollow rail and stile bulb at a sash corner. It even documents placing part of a short foam segment into the rail and the rest into the stile bulb. This is strong evidence that the foam is a junction component, rather than a generic long-length gasket. [S:AND400CORNER] It is not evidence that any household foam plug is acceptable or that a specific size applies to your unknown sash.
Inspect without removing the sash
Close and reopen the unit normally if it operates freely. Take a photo of the entire gliding window showing the sliding and fixed sides, then one photo at each corner where the missing material is suspected. Mark top-left, top-right, bottom-left, bottom-right on a sketch and record which corner is actually affected. A missing seal is easier to identify by comparing the other corners than by stretching or removing intact foam. If debris is visible, make a note; avoid tools that damage the rail or stile receiver.
Before an order, identify 400 Series by actual product information: this article does not apply automatically to 200 Series check-rail bulbs or all Perma-Shield gliders. A photograph of a gap along the sash edge alone cannot establish the intended repair material.
What the original instructions require beyond identification
The manufacturer's replacement procedure references removal of the active/passive sash and a specific foam insertion approach. [S:AND400CORNER] This page is deliberately an identification guide. Heavy glazing, elevated windows and unsupported sash removal are not appropriate for improvised DIY testing. Ask Andersen whether a service provider is appropriate before removing the sash.
Send Andersen: series and approximate production era with source, whole unit image, damaged corner close-up, state of nearby rail/stile seals, and a count of foam junctions still present. Ask whether a corner-foam kit or a different part is called for, and whether other edge seals also require attention.
Original evidence and uncertainty
Andersen Help Center 000005103, Corner Foam Weatherstrip for 400 Series Gliding Windows, Details and Replacement Instructions; accessed 2026-10-12: manufacturer. For context, Andersen's Air Infiltration in Andersen Gliding Windows, 400 Series navigation, manufacturer. Original 69 draft NW0039 is specifically about frame head/sill plugs. This proposal owns only sash corner foam versus edge seal.