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Foam fill

Also called foam insulation

Insulating foam that fills the hollow of a frame member.

Air in a large hollow can circulate and carry heat across it. Filling the hollow with foam, usually polyurethane, stops that.

Foam is common in fiberglass windows, whose sections have a few large hollows, and is an upgrade in some vinyl ones.

Bottom rail of a fiberglass sash in section, outside at left

Hover or tap a part to see what it is called.

Fiberglass sash, bottom rail in section

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