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Greenhouse polycarbonate: thickness, twin-wall and multiwall are not the same specification

Research review: September 19, 2026 · Source-based editorial analysis

A useful glazing comparison records the material, wall construction and thickness for each part of the greenhouse. One headline number often misses the actual purchase.

Start with the envelope schedule

Write separate lines for roof, main walls, doors and windows. The Bella listing describes 6 mm walls and roof but 4 mm door and window panels. The Balance uses twin-wall roof panels and crystal-clear walls. Labeling either model with a single generalized panel description would remove information the buyer needs. [Source]

Preserve the manufacturer’s terminology

The Glory description specifies 10 mm twin-wall panels while the page also uses a Multiwall heading. Rather than silently treating those terms as a count of additional layers, we preserve the wording and point to the model source. When the number or structure of internal walls matters to your decision, ask for the actual panel specification or section drawing. [Source]

Thickness is not a complete heating input

Our heater-sizing tool asks for an explicit U-factor. It does not use a dropdown that assigns an unverified thermal number to every 4 mm, 6 mm or 10 mm panel. That is intentional: the purchasing description and the needed heat-transfer input are not the same field. Obtain the documented assembly value in the correct units before treating the estimate as a meaningful comparison.

Watch the unit when comparing film kits

Bootstrap Farmer lists 6 mil film for the reviewed hoop-house kit. A mil is one-thousandth of an inch, not a millimetre. A 6 mil film covering must not be entered in a comparison as a 6 mm rigid panel. Keep the covering system and the unit together, including in any supplier spreadsheet you use to compare offers. [Source]

Area is not an order quantity

The panel-area calculator can estimate the gross surface area of a simple gable greenhouse. It does not know the panel sizes available, the orientation required by the manufacturer, the cutting layout or the amount of usable offcut. For a branded kit, start with the exact replacement-panel schedule. For another design, have the supplier confirm the appropriate product and ordering plan instead of buying solely from a gross-area result.

Planning guidance only. Manufacturer documentation, local building requirements and qualified professionals control final structural, electrical and gas installation decisions.

Turn the guide into a buying decision.

Compare assumptions with the greenhouse heating benchmark and downloadable data. Its results describe hypothetical gable structures, not independent tests of the products in our catalog.

Compare the greenhouse kits and buying constraints →