Multiwall Polycarbonate

Multiwall polycarbonate glazing sheet is a high quality product produced in 'clean-room' conditions which helps to ensure that it retains its quality.

It is an ideal roof glazing material that offers remarkable impact resistance and long-term weather durability. It is virtually unbreakable and will withstand storms, hail-stones, wind, snowfalls and ice formation - as well as prolonged hot sunny weather. It performs extremely well in temperatures as low as -40 degrees C and as high as +120 degrees C.

In addition, it has high levels of light transmission and superb heat insulation characteristics, both of which offer cost savings by conserving energy - important when we are all trying to cut down on carbon emissions. Multiwall polycarbonate is also very light in weight compared with glass, making it much easier to lift on to a roof. Because it is so tough there will be no breakages during installation, and being light in weight means that it doesn't need heavy structures to hold it in place.

As well as the standard clear product, multiwall polycarbonate can also be supplied in opal or bronze tints, and a Venetian pattern (a thin white stripe). These tints/patterns are for use where levels of light transmission and/or solar heat gain need to be restricted, such as applications on a south or west facing roof.

The product features a proprietary UV coating that is designed to protect the sheet against the degrading effects of ultra-violet radiation in natural sunlight. UV will not be transmitted through this glazing, making it an ideal choice for playground canopies used to protect children from these harmful rays.

Typical applications where multiwall glazing is used include:

  • Industrial and commercial rooflights
  • School playground canopies and covered areas
  • Stadia roofing
  • Railway station and platform canopy roofing
  • Commercial greenhouses
  • Swimming pool roof covers
  • Partition walls
  • High level vertical glazing
  • Smoking shelter roofing
  • Greenhouses

It is also widely used in the domestic market for:

  • Conservatory roofing
  • Car ports
  • Patio covers
  • Sun room roofing
  • Cloches
  • Home greenhouses (where its unbreakability provides safety to young, playing children)

Impact Resistance

Despite its light weight, multiwall polycarbonate is much tougher and stronger than glass. It is virtually unbreakable and can withstand heavy storms, hailstones and snow.


At Twinfix we supply multiwall polycarbonate that has a UV coating. This protects if from the degrading effects of ultra-violet radiation in natural sunlight. Whilst our 16mm and 25mm sheet are coextruded with a UV-protective layer to both sides other thicknesses have only one side with this protection. This UV-protected side must face upwards/outwards when installed.


Care must be taken when handling and installing multiwall polycarbonate sheet in order to prevent damage. Each sheet is protected on both sides with a masking film. The film should remain on until installation. You should never use a craft knife to remove the film, as this will damage the surface. Simply peel the masking film away from edge where it will be covered by the glazing bars and remove it completely once installation is complete. Do not leave it in place once installation is finished. Sheet should be cleaned with warm soapy water, never use abrasive detergents or proprietary cleaning products.


Multiwall sheet is designed to be installed with the flutes going down the slope of the glazing, i.e. from ridge down to eaves, and not across.

Similarly when cold-bending multiwall sheet the flutes must be parallel to the bend or the sheet could be at risk of buckling.

Twinfix Service

We will cut your multiwall glazing to size: even to shape as long as we have all the information to work to. After cutting, we will blow the flutes free of swarf and dust. We will then tape the ridge end of the sheet with an aluminium blanking tape and the eaves end of the sheet with an anti-dust breather tape (grey in colour). This helps to keep the sheet free from dust and crawling insects in the future.

We usually deliver this product on our own vehicles, with our own team of drivers, but where this is not possible we will on occasion send out orders via a courier service. You can, of course, collect direct from our Warrington facility, should you wish.

Help & Advice

If you have a project in mind or would like help or advice on any of our products or services, please either ring us on 01925 811311, email us at or get in touch via the enquiry form on our Contact Us page.


Related FAQs

1. What thicknesses, sizes and colours are available in multiwall polycarbonate?
We can supply you from stock in 6mm, 10mm 16mm and 25mm thicknesses. Many different sheet sizes are available up to 7 metre x 2.1 metre, but not every thickness is available in every size so it is always best to check with our sales office. In 10mm, 16mm and 25mm we can supply clear, opal and bronze variants. We will also be launching 32mm in the very near future.
2. What is Venetian polycarbonate?
Lexan Thermoclear Venetian is a multiwall sheet which has been screenprinted with white stripes on the non-uv coated side. The white stripe should always be installed facing inwards, the other side, clearly identified as protected against UV, being installed facing outwards. The white stripes are primarily there for decoration but they also help in reducing glare and heat build up inside a room.
3. What is the minimum pitch for a polycarbonate roof?
Never install polycarbonate flat. Our standard glazing systems require a minimum pitch of 5° to ensure water can run off the roof and to eliminate ‘puddling’. Our Multi-Link-Panel modular system should be installed with a minimum 10° pitch. Contact us if you require clarification.
4. Can you walk on polycarbonate sheet?
Polycarbonate has been tested against UK wind and snow loads and we can supply you with recommended glazing centres for each thickness of polycarbonate. However you should never walk directly on polycarbonate sheet. A crawling board or similar should be placed across at least two structural supports of the roof. We can manufacture aluminium framed polycarbonate panels which have been tested for non-fragility to ACR(M)001:2014 – this does not mean you can walk on the polycarbonate but gives added resistance to accidental falls.
5. How do you cut multiwall polycarbonate sheet?
Multiwall polycarbonate can be cut easily and accurately with standard workshop equipment including common circular, hand and hacksaws. When cutting multiwall polycarbonate saw dust should be blown out of the flutes using dry compressed air. Circular saws should have fine-toothed blades. If you are cutting with hand or power hacksaws always make sure the sheet is clamped to a worktable. After cutting and blowing air through the sheets, the flutes should be taped with an anti-dust breather tape at the eaves (lower) end of the roof and with a blanking tape at the ridge (upper) end.
6. How do you fix multiwall polycarbonate sheet?
We can supply you with glazing systems to secure the polycarbonate to your roof depending on the type of roof you have. We have rafter gasket systems for fitting onto rafters or structural systems to fit across purlins and even systems that can span up to 4 metres between fixing points. We also carry the accessory trims and profiles needed to finish the roof of as well as many of the fixings needed to secure the glazing system to the supporting structure.
7. How much allowance do I leave for expansion and contraction?
Thermal expansion of the sheet is 3mm per linear metre. When you talk to us about your application, we will quote you the recommended glazing centres and quote you the cut width of the polycarbonate sheet which allows for the expansion and contraction.
8. How do you clean polycarbonate sheet?
Gently wash the sheet with a solution of mild soap and lukewarm water, using a soft, grit free cloth or sponge to loosen any dirt or grime. Rinse over with clean water to remove any residue. NEVER use a proprietary glass cleaner.
9. What is the life span of multiwall polycarbonate sheet?
The manufacturers of multiwall polycarbonate sheet offer a ten year written limited warranty on the product which covers discolouration, loss of light transmission and loss of impact strength due to weathering. That does not mean that after 10 years the sheet will fail, we have installations that have been in situ longer than 10 years with no obvious detrimental affect either in appearance or performance.
10. How much light does multiwall polycarbonate let through?
Taking 16mm triplewall polycarbonate as an example, clear sheet has a light transmission of 74%, opal has 62% and bronze has 30%
11. What is the fire performance of polycarbonate?
Polycarbonate has good fire behaviour characteristics and receives high ratings in several major European fire performance tests including EN13501. Always check with the Twinfix sales office for current classification, at the time of writing most variants achieve a class1Y when tested against BS476 part 7 surface spread of flame.
12. How does UV affect polycarbonate?
Solar radiation has a particularly harmful effect upon materials that are not protected. Many variants of multiwall polycarbonate have a unique proprietary UV-protected surface on one or both sides, giving excellent resistance to outdoor weathering. This unique protection ensures long-term optical quality under intensive UV exposure.
13. What centres should I be using when glazing multiwall polycarbonate on a roof?
Although it is made in very wide panels, multiwall polycarbonate is only lightweight and as such there are maximum widths it should be glazed at, based on UK wind and snow loadings, as follows:
10mm = 700mm wide panels
16mm = 1000mm wide panels
25mm = 1250mm wide panels
14. Polycarbonate is virtually unbreakable, so isn't polycarbonate glazing non-fragile?
No, in many canopies that use multi-wall or solid polycarbonate glazing, the glazing is simply clamped into a glazing bar system that just holds these sheets in place. Whilst the sheet itself might not break, a falling object, (and in some cases even a strong wind), can flex the sheet and force it out from between the glazing bars. If someone were to trip on such a roof, they could fall through, endangering themselves and anyone underneath. Remember..... just because it doesn't break doesn't make it non-fragile.