Yes, into glass, with an adaptor and a hole cut by a glazier — the size comes from the manufacturer’s template, and on a double-glazed unit it means a new pane.
Glass is a common route and the one with the least room for error.
Why a glazier
A hole cut in a sealed unit destroys it. The pane is replaced with one cut to the flap’s template, which is a made-to-order item.
The adaptor
Flaps designed for door panels need a glass adaptor to seal against a thin, flat surface. It is a separate purchase, like the tunnel extenders for walls.
Position
Low is better for the cat, and low in a window usually means the bottom pane. Consider what is directly outside — a drop, a bin, a road.
Security
A hole in a ground-floor window is a hole. Weigh it against the door option before committing, because the pane is not reversible.
This does not replace your device’s manual. Blade temperatures, locking mechanisms and cleaning procedures differ from model to model, and the manufacturer’s instructions take precedence over anything written here. Unplug a device before dismantling it, check a hot blade or an air nozzle against your own hand before it goes anywhere near an animal, and keep a mechanism that closes or rotates under supervision until you know how it behaves.
Last reviewed 2026-08-17