uPVC windows for Indian buildings.

A sliding panel runs along a track and never swings into the room. A casement sash is hinged and presses onto its gasket all the way round when you close it. That difference in how they shut is the reason a casement usually seals more tightly, and the reason a slider suits a wide opening or a tight balcony better.

Decide that first. Once it is settled, the remaining choice is depth and chamber count, and there are only two options on each side.

Depth is the front-to-back measurement of the section, in millimetres. A deeper section has more room inside it for chambers, for steel reinforcement and for larger glazing units. Chambers are the hollow cells within that section. They hold still air, which slows heat moving through the frame, and they stiffen the profile.

Neither number is a performance figure on its own. A five-chamber profile in a badly fabricated frame will underperform a three-chamber profile in a good one. Ask for both the section and the fabrication standard.

TruFrame manufactures the profile at the works in Lucknow and supplies it in lengths to fabricators. The fabricator cuts, reinforces, welds, glazes and fits hardware. An installer fixes the finished unit into the wall and seals the joint.

This matters when something goes wrong, because the three stages are warranted by different parties. Ask who is responsible for the joint between window and wall before you order.