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Twinwall vs solid polycarbonate

Updated: October 2026

You are choosing a sheet for a greenhouse roof or a clear panel beside a door, and both are called polycarbonate. Twinwall vs solid polycarbonate is a choice about structure. Twinwall is two skins with air in the flutes. Solid sheet is a clear plate. One holds heat and shows stripes. The other looks more like glass, weighs more, and lets heat through. This page does not rank the eight listings. Those sit on the [twinwall polycarbonate comparison](/hub/diy-supplies/twinwall-polycarbonate). Peter F. used UK merchant tables, dated 16 October 2026. We did not run a U-value test. If you buy through our links, a qualifying purchase can earn us a commission at no extra cost to you.

You are choosing a sheet for a greenhouse roof or a clear panel beside a door, and both are called polycarbonate. Twinwall vs solid polycarbonate is a choice about structure. Twinwall is two skins with air in the flutes.

Our top picks

Warmfay Warmfay 10-pack 4 mm

Best overall

Warmfay Warmfay 10-pack 4 mm
5.6/10about £54.99
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TEOV TEOV 14-pack 4 mm

Rank 2

TEOV TEOV 14-pack 4 mm
6.8/10about £62.29
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CHEOAR CHEOAR 10-pack 4 mm

Alternative

CHEOAR CHEOAR 10-pack 4 mm
6.0/10about £61.99
View offer
On this page
  1. 1.What is different in the sheet
  2. 2.Heat, light, and weight
  3. 3.Greenhouse, window, or roof
  4. 4.What neither sheet is

What is different in the sheet

Twinwall is two skins and a row of ribs. The flutes are the insulation, and the channels you have to tape. You see those ribs as fine lines. Cut the sheet and the ends are open. Solid polycarbonate is a plate of the same plastic without the air gap. At the same nominal thickness it is clearer, heavier, and a poorer insulator. There is no flute to tape. Twinfix states UV on both sides of its 6 mm solid sheet. A twinwall bullet that says both sides is a different claim, on a hollow board. Acrylic and a 1 mm film are neither. The generic 1 × 3 m listing at £51.99 never says twin-wall or a thickness, so it is not evidence for either side. The useful differences are brand tables.

Heat, light, and weight

UK merchants repeat Palram’s clear twinwall figures. At 4 mm: about 82% light, U-value 3.8, about 0.8 kg/m². At 6 mm: about 80% light, U-value 3.5, about 1.3 kg/m². At 10 mm: about 79% light, U-value 2.9, about 1.7 kg/m². A lower U-value is the better insulator. Opal 10 mm on that line is about 30% light, a shade rather than a crop sheet. Twinfix publishes 6 mm solid at 7.2 kg/m² and 85% light, with UV on both sides of that product. Palram’s 6 mm twinwall is 1.3 kg/m² and about 80% light. The plate lets a bit more light through and weighs about five times as much. Twinfix does not print a U-value on the page we checked, so this guide does not invent one. Take the air gap when warmth matters, and the plate when you want the view.
Warmfay Warmfay 10-pack 4 mm

Testsieger

Warmfay Warmfay 10-pack 4 mm
5.6/10about £54.99
View offer

Greenhouse, window, or roof

For a UK greenhouse, twinwall is still the usual pane. The Polycarbonate Store treats 4 mm as the everyday sheet, and solid around 2–6 mm as more light and less insulation. Varico’s line is the one to keep: multiwall on a roof, solid when the pane must look glass-clear. Choose twinwall when the house has to hold heat and you can live with stripes. A 4 mm pane in a 4 mm clip is the ordinary reglaze if the width matches, which is the subject of the polycarbonate greenhouse panels page. Choose solid for a view or a sidelight, and accept the weight and the heat loss. Omega’s W-clip is stated for 3 mm glass or 4 mm twinwall, so 6 mm solid does not belong in it. Hole size is on how to fit twinwall polycarbonate. Solid does not need flute tape.

What neither sheet is

Neither sheet is a floor. Do not walk on twinwall, and do not walk on solid sheet because a listing says it is stronger than glass. Twinfix warns that solid sheet can leave the bars without shattering. Stronger than glass means impact compared with horticultural glass, not a surface you can stand on. Approved Document B allows a TP(a) route for solid polycarbonate at least 3 mm thick, and excludes multi-skinned sheet. Twinwall is not automatically TP(a). If the title never says twin-wall or a thickness, you are not ready to choose either structure. Read thickness and span on the buying guide once you know you want the flutes.

Common questions

Which is warmer?
Twinwall. Palram’s figures give clear twinwall a U-value of 3.8 at 4 mm, 3.5 at 6 mm, and 2.9 at 10 mm. A lower number holds more heat. Twinfix does not print a U-value for 6 mm solid on the page we used, so we do not invent one. Installer notes say single-wall lets heat go and twin-wall keeps it.
Which lets in more light?
Solid, by a small margin at the same thickness. Twinfix states 85% for 6 mm solid. Palram’s 6 mm clear twinwall is about 80%. The large light loss is colour: opal twinwall at 10 mm is about 30%. For crops, clear twinwall is the usual choice. For a stripe-free view, solid is the one.
Which is lighter to handle?
Twinwall. Palram’s 6 mm twinwall is about 1.3 kg/m², and Twinfix’s 6 mm solid is 7.2 kg/m². A square metre of the plate is several times the lift, and that weight stays on the greenhouse bars after you have fixed it.
Can I use solid sheet in the same greenhouse clips?
Only if the clip is made for that plate. Omega’s W-clip is stated for 3 mm glass or 4 mm twinwall, so a 6 mm solid sheet is outside that sentence. Matching the word polycarbonate on the title is not the same as matching the rebate.
Does stronger than glass mean I can walk on it?
No. The phrase compares impact with horticultural glass. Twinfix warns that solid polycarbonate can leave the bars without shattering under you, and twinwall is not a floor either. Work from a board that bears on the frame, or from the ground.
Is 4 mm twinwall always too thin?
No. It is the usual UK greenhouse pane, and makers still sell it for greenhouse beads. It is too thin for a canopy span that trade guides rate from 10 mm, and it is the wrong sheet if you need a stripe-free plate. One seller calling it flimsy does not retire it from a 4 mm clip.

Related pages

Best twinwall polycarbonate in this set

Twinwall polycarbonate

Twinwall polycarbonate sheets: what to order in the UK

Polycarbonate greenhouse panels that fit the frame

How to fit twinwall polycarbonate on a UK greenhouse

Sources

Public UK sources on the product standard, fire classification, outbuildings, and the description of goods. Prices, stars, and review counts are the amazon.co.uk figures in the extracts. The Polycarbonate Store prices are from 16 October 2026. Prices move.

  1. BS EN 16153:2013+A1:2015, light-transmitting flat multiwall polycarbonate sheets (retrieved 16 October 2026)
  2. Approved Document B, 2025 amendments (retrieved 16 October 2026)
  3. GPDO 2015, Schedule 2, Class E, buildings incidental to a dwellinghouse (retrieved 16 October 2026)
  4. Consumer Rights Act 2015, section 11, goods to match the description (retrieved 16 October 2026)
  5. Palram SUNLITE technical guide (retrieved 16 October 2026)
  6. The Polycarbonate Store, twinwall polycarbonate (retrieved 16 October 2026)
  7. Marlon ST installation guide (retrieved 16 October 2026)
  8. Omega greenhouse glazing W spring clip, pack of 100 (retrieved 16 October 2026)