Double glazing contributes a lot to this, but there are other things that can help as well.
The windows we have chosen are all double glazed and also thermally broken. This means that the frames also help to maintain temperature unlike standard aluminium windows which conduct heat in and out of buildings constantly. Our windows are made from UPVC which along with wood frames are the best choices - with sustainably sourced timber probably the better option. UPVC however, not requiring painting, are a lower maintenance option. Additional to this, we also have Argon gas between the two glass layers. This is a transparent gas that again helps prevent the disbursement of heat.
The compromise we had to make for our window selection was we couldn't quite get the styles we wanted. Ideally we preferred to have double hung windows, but getting these in UPVC proved quite a challenge. There was one company who could do this - but they couldn't provide flywire for our high light windows and a retrofit option was not available. Their price was considerably higher too. So we have many Tilt & Turn windows - also known as European windows. These have two ways of opening. One like a door which opens wide, and the other where the bottom locks down, and the window tilts back leaving a gap at the top. I'm really happy with the windows we have chosen, I just wish I had paid more attention to which way they open as I should have had a couple opening in the opposite direction.
|Tilt & Turn window closed. Without flywire looks like a door|
|Tilt & Turn fully open (should have had this one open the other way)|
|Tilt & Turn window at tilt|