Polycarbonate is around half the weight of glass, when you compare screens of the same thickness. So a 5mm thick glass door window weighing 5kg will drop to 2.5kg when made from polycarbonate.
Below are a few examples of actual savings attained on a BMW E92 Coupe:
Glass windscreen – 11.5kg
Polycarbonate windscreen - 5.85 kg
Glass door window – 4kg
Polycarbonate door window – 2.1kg
Glass rear quarter window – 1.95kg
Polycarbonate rear quarter window – 1.0kg
Glass rear screen – 6.8kg
Polycarbonate rear screen – 3.3kg
Total weight of all glass on car = 30.2kg
Total Weight of all Polycarbonate on car 15.35kg
Weight saving of 14.85kg
Added to this is also around 20 kg of additional savings due to removal of the window motors, all the heavy rubber seals and fixings that are not needed with Polycarbonate replacements.
How to calculate your weight savings
A simple calculation you can use to get the weight of replacement polycarbonate:
Weight of your glass window divided by the thickness of the glass = X
Thickness of Polycarbonate you require = Y
Multiply Y by X then divide the answer by 2 to give you approximate weight of Polycarbonate.
Y x X ÷ 2 = approx. weight of Polycarbonate window
Window weighs 10kg and is 4.3mm thick.
10kg ÷ 4.3 = 2.32kg
(4mm polycarbonate required)
2.32kg x 4 = 9.28kg - this gives you the glass weight if the glass window was 4mm thick.
9.28kg ÷ 2 = 4.64kg - half the given glass weight of 9.28kg, giving us a weight of 4.64kg for the equivalent Polycarbonate.