Virginia Tech Extension lists visible-light transmittance ranges of 85% to 87% for single-layer polyethylene film, 74% to 77% for double-layer film, about 83% for bi-wall polycarbonate and 88% to 94% for standard glass. These are material examples, not a guarantee for every product; thickness, coating, frame and installation change the result. Compare the exact light and insulation specifications with your crop, climate, framing and replacement plan.
The frame type answers how a greenhouse is built; its covering determines a separate set of choices about transmitted light, insulation, service life and support. Match the exact panel or film with the crops and the structure’s installation instructions.
Compare common cover materials
| Cover | What to compare | Source-backed example |
|---|---|---|
| Single-layer polyethylene film | UV treatment, attachment, replacement access and wind exposure | Virginia Tech lists 85% to 87% visible transmittance in its table |
| Double-layer polyethylene film | Inflation or air-space design, fan requirements and light tradeoff | Virginia Tech lists 74% to 77% visible transmittance in its table |
| Multiwall polycarbonate | Panel thickness, wall structure, fasteners and expansion allowance | Virginia Tech describes a bi-wall example at about 83% visible transmittance |
| Glass | Panel support, safe installation, seals and replacement access | Virginia Tech lists 88% to 94% visible transmittance for standard glass |
The figures come from Virginia Tech Extension’s material comparison. They describe examples, not the performance of every brand or thickness. Purdue Extension also compares glazing options and emphasizes matching greenhouse construction to the site and growing conditions.
Balance light and insulation
Visible transmittance estimates how much visible light passes through a cover. A higher figure can be useful for light-demanding crops, but it does not describe every light wavelength or account for shade from the frame, dirt, condensation and installation. Use the manufacturer’s data sheet for the exact product, and consider the crop’s light needs across the season.
Multiwall panels and double-layer film can provide a different insulation profile from a single sheet, but the supporting frame and installation must suit the system. Virginia Tech notes that polycarbonate expands with temperature; follow its fixing and expansion instructions so panel movement is allowed for. Check each maker’s guidance for cleaning, ventilation, UV protection and replacement.
Match the cover to the structure
Before buying a replacement or complete kit, verify the frame span, panel or film dimensions, attachment system, local wind and snow exposure, vents and door details. A cover that fits on paper may still require specific supports, fasteners or spacing. Ask the local building office about permits and setbacks for a permanent structure.
First choose the structure that fits the growing space in the greenhouse kits vs. hoop houses comparison. For an indoor seedling station before plants move under cover, compare seed-starting lights and heat mats. Browse food garden guides.
Sources
Common questions
Which greenhouse covering lets in the most light?
Virginia Tech Extension lists standard glass at 88% to 94% visible transmittance in its comparison, while product-specific polycarbonate and polyethylene figures vary. Check the exact panel or film data sheet and the light needs of the crop.
Is double-layer greenhouse film better than single-layer film?
A double layer can improve insulation when installed as designed, but the Virginia Tech table lists lower light transmittance than its single-layer film example. Compare both light and heat needs for your setup.
How long does greenhouse plastic or polycarbonate last?
Published estimates vary by material, UV protection, climate and installation. Compare the specific warranty, replacement guidance and support instructions rather than relying on one lifespan for every cover.
Can I put any greenhouse cover on an existing frame?
No. Confirm the cover dimensions, attachment method, frame spacing, wind and snow requirements, and any expansion allowance in the frame and covering instructions.