Direct answer: combine profile, glass, airtightness and installation
In cold areas, the window must reduce heat loss, air leakage and cold surface sensation.
Profile insulation
Aluminium should include thermal break; PVC can offer strong insulation, but system quality still matters.
Low-e glass
Low-emissivity glass is usually one of the most important choices in cold climates.
Airtightness and installation
Poor sealing around the frame or shutter box can waste the performance of the best glass.
Common mistakes
Comparing only unit price.
Choosing basic glass.
Ignoring the shutter box.
Forgetting perimeter sealing.
Practical recommendation
Ask the quote to detail profile, glass, shutter box, installation and trims.