HILLMAN - Imp - Hardcoated Lexan Polycarbonate front windscreen

Frequently Asked Questions

Why should I use Lexan Polycarbonate windows?

We have been making Lexan Polycarbonate windows for motorsports applications for over 20 years. Lexan Polycarbonate windows have been popular in motorsports for much longer, and for good reason! To this day, you will find Polycarbonate windows in abundance at events ranging from amateur track days to the FIA World Rallycross Championship, in specially built cars driven by the best drivers the world over. But why do they deserve a place in your next car build?

The first and biggest advantage of Lexan Polycarbonate windows is weight savings. In professional motorsports applications, every kilo matters. Polycarbonate windows provide approximately 50% weight savings versus the OEM glass of the same thickness. And, thanks to our Thermoforming process, our windows fit the OEM glass curvature perfectly and can even work with window winding mechanisms if needed. Furthermore you can expect to see additional weight savings due to removal of the window motors, all the heavy rubber seals and fixings that are not needed with Polycarbonate windows.

Polycarbonate windows are 250x stronger than glass windows. In the unfortunate event of an accident, Polycarbonate windows remove the risk of glass shards spreading throughout the cabin and potentially causing injury to the driver and safety personnel.

Polycarbonte windows is the design freedom they provide. Unlike glass, Polycarbonate can be cut to accomodate air scoops and ducts, as well as window sliders without compromising the rigidity of the window. This can prove especially beneficial when cutting air scoops into the engine cover window in mid engine cars, directing additional airflow straight to the engine; or allowing louvers to be cut into rear quarter windows. We are also able to print OEM quality black borders and dot matrix seriography directly on to the Polycarbonate, so they are identical to the OEM glass. All of our windows are also UV protected from our factory in order to minimise the risk of UV sunlight discolouring as much as possible.

Which thickness should I choose?

3mm - 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.

4mm - 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.

5mm - thick and heavy duty windows. We usually would use 5mm on frameless door windows or for some vintage race cars with big curved rear screens.

More information can be found here.

Are your windows curved and pre-cut to fit?

Yes, all of our windows are trimmed to the size of the stock windows. However, there are a few exceptions where we deliberately make the windows a little bigger in order to fit where body trims are bonded to the glass, but we can not add them to the polycarbonate.

All of our windows are also pre-curved to the curvature of the original glass.

Can I use the original window mechanism?

Yes. As all of our windows are direct OEM window replacements, you can wind our windows up and down. We highly recommend you choose our hardcoating option if you intend to use the original winder mechanism, otherwise your window will scratch with immediate use. Please also ensure any rubber seals are free of grit/ debris or these will also scratch your windows.

Do your windows come with black borders?

Yes.

If your OEM windows came with black borders from factory then your polycarbonate windows will come with black borders pre-applied. We will even add a dot matrix if the original glass had one.

How do I fit my Lexan Polycarbonate windows?

We have written guidelines for fitting your windows,which you can find here.

We have also produced a short video to show you how to bond our rear screens and quarter windows to your car,which you can find here.

Do not be tempted to use any glues or primers that are designed to bond glass windows into cars. These primers and cleaners are too aggressive for polycarbonate, and the typical glass adhesive does not allow for expansion in the polycarbonate. These will damage your windows.

Are your windows FIA/ MSA approved?

The FIA/ MSA or other regulatory bodies do not actually ‘approve’ any manufacturers' windows. The FIA / MSA publish a set of requirements that windows must be made to, and this usually involves using a recognised shatterproof material of a certain thickness and permanently marked to indicate this.

All of our Polycarbonate products meet all the current material specifications for construction from a shatterproof plastic, and we can provide thickness’s to suit the required regulations. Our windows are permanently marked with the appropriate material specifications and ID numbers required.

How much weight will I save?

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

Example

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.

Which is the best type of Polycarbonate for my windows?

We often get asked which is the best type of polycarbonate; Lexan or Makrolon or Arla? It’s a difficult question to answer.

For you, the Customer, there is no difference other than the brand name. All companies produce top quality polycarbonate and they are more than suitable for use in your vehicle.

Is Polycarbonate the same as Lexan, Makrolon or Arla?

Yes! Lexan, Makrolon and Arla are all brand names of polycarbonate sheet & resin manufacturers. For us, the window manufacturer, each brand of polycarbonate has its benefits during manufacturing and the supply of the brands also dictates which material we tend to use.

As Makrolon is not the easiest of materials to get in the UK at the moment, we use Polycarbonate from Lexan in the Netherlands and Arla in Sweden.

Can I wind the windows up and down?

Yes! As our windows are direct replacements for the glass they will fit to the electric or manual winder mechanisms, however we recommend you choose the hardcoated polycarbonate as regular polycarbonate will scratch very easily. They don’t come with any of the window fitting tabs or fixings though.