Which thickness should I choose for my Lexan Polycarbonate windows?

"Which window thickness do I need?" is probably one of our most asked questions, so we will try to give you some guidelines. Our windows are available in 3mm (1/8 Inch), 4mm (5/32 Inch) & 5mm (13/64 inch) and we also have front windshields available in 5mm (13/64 inch) and 6mm (1/4 inch).

We also have high tolerance polycarbonates available in 3.2mm, 4.2mm, 5.2mm & 6.2mm, used when FIA regulations require a minimum thickness material - please ask.

There are manufacturing tolerances in the thickness, so you will usually find the windows to be slightly under the advertised thickness -with the exception of our front windshields which are always slightly over the advertised thickness (to meet a lot of the FIA minimum thickness regulations).

3mm – 1/8 inch  - Lightest and most flexible

This is our lightest and most flexible choice. It is a good choice for when you are bonding or bolting windows into the car like the rear screen and rear quarter windows, or if you are going to permanently fix the door windows into the doors. We would not recommend using 3mm if you want to roll door windows up and down or you have a large flat rear screen or you are installing the windows into an older car with rubber seals.

4mm – 5/32 inch - Good all-round thickness

The best all-round thickness choice. 4mm gives you good weight savings and also remains fairly rigid so you can use it for any bonded or bolted in windows or windows fitted into rubber seals as well as the majority of door windows – this is usually our recommended thickness.

5mm – 13/64 inch - Heavy duty

Thick and heavy duty windows. We usually would use 5mm on frameless door windows such as the Subaru Impreza’s or the Nissan S13, 14, 15s etc. or for some vintage race cars with big curved rear screens. Other than that, unless your regulations require 5mm, then it is a bit thick and unnecessary.


Windshields – 5.1mm & 6.1mm 

As these are made from a special polycarbonate, we make sure they are manufactured over thickness so that they will always meet the FIA’s minimum thickness regulations of 5mm and 6mm.

With windscreens, you must consider the wind loading at speed which can cause the screen to flex and vibrate, so we would always recommend 6.1mm on cars running high speeds with big or fairly flat windscreens. We recommend dropping to 5.1mm on smaller saloons and hatchbacks. The screens can also be braced down the centre if your regulations allow, meaning you can go for the lighter 5mm. 


Just ask us if you need any further advice regarding what thickness to use.

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