10th May 2022, 07:06 PM
Filling the gap keeps wind out and heat / cold in. You only get one chance so make the most of it!
On one window I used a ‘low expansion’ expansion foam - but it was quite expensive.
So on some other windows I used insulation scraps.
On some other gaps I used foam (either the extruded foam that comes in a long tube shape - or grey foam expansion joint, cut slightly oversize and squeezed in the gap.