Acrylic Greenhouse Panels vs Polycarbonate

Short answer: For most greenhouse roofs and walls, use a multiwall panel, not single-sheet acrylic. A single sheet transmits about 92% of light but insulates no better than single glass. Twin-wall polycarbonate (about 80% light, U-value about 0.58 for 8 mm) is the usual budget choice. Multi-skin acrylic such as Acrylite Alltop (up to 91% of plant light, U-value 0.44 for 16 mm) is the premium one. Flat single-sheet acrylic is best for cold frames, windows, doors, and propagation covers.

Key facts

Single-sheet clear acrylic: about 92% light transmission. As a single pane its U-factor is only about 10% better than glass (Acrylite), so it loses heat fast on cold nights.
Twin-wall polycarbonate: Palram lists its 8 mm twin-wall at 80% light transmission and a U-value of 0.58 Btu/h·ft²·°F. Its 16 mm triple-wall is 76% and 0.42.
Multi-skin acrylic: Acrylite says its multi-skin passes up to 91% of photosynthetically active radiation (PAR). Its 16 mm sheet has a U-value of 0.44, against 1.0 for single glazing. Acrylite claims 89% light for 16 mm Alltop vs 72% for 16 mm polycarbonate.
Warranties (Acrylite greenhouse sheet): 30 years against yellowing, 10 years on light transmission, and 10 years against hail. All are prorated. Palram gives its multiwall polycarbonate a 10-year limited warranty.
Expansion: about 0.2 in. per 48 in. over a 100 °F swing (Acrylite).
UV: standard clear acrylic passes very little UV below about 345 nm. UV-transmitting grades such as Acrylite Alltop UV Transmitting and Plexiglas XT 0A370 pass it.

Acrylic or polycarbonate for a greenhouse?

Here's how the common glazing options compare. Figures are maker data for the named products; other brands and thicknesses differ.

	Single-sheet clear acrylic	Twin-wall polycarbonate (8 mm)	Multi-skin acrylic (16 mm)	Single-pane glass
Light transmission	About 92%, perfectly clear	About 80%, diffused	Up to 91% of PAR (maker figure)	Roughly 85 to 90%, varies by glass
U-value (Btu/h·ft²·°F; lower insulates better)	About 1.0, a little better than glass	About 0.58	0.44	About 1.0 or more
Hail and impact	Good, but large hail can crack flat sheet	Excellent	Standard grades good; high-impact grades with 10-year hail warranty	Poor
Yellowing	Doesn't yellow (30-year maker warranties on clear)	Relies on a UV-protected face; 10-year warranty typical	30-year non-yellowing warranty	Doesn't yellow
Weight	Half of glass	Very light	Light	Heavy

Insulation usually decides it. A greenhouse loses most of its heat through the glazing on cold nights. Acrylite's numbers put 16 mm multi-skin at less than half the heat loss of single glazing (U 0.44 vs 1.0), and the maker claims more than 40% energy savings. Twin-wall polycarbonate at about 0.58 is a big improvement too. Diffused light from multiwall panels also cuts hot spots and reaches lower leaves.

So the real choice for a roof is twin-wall polycarbonate or multi-skin acrylic, not flat acrylic sheet. Polycarbonate is cheaper and tougher. Multi-skin acrylic lets in more light and keeps it longer: Acrylite says its sheet still transmits more light after 10 years than new polycarbonate does. Multi-skin panels come from sheet makers in 8 to 28 ft lengths. We don't cut them; we cut flat sheet.

When does flat acrylic sheet make sense?

Cold frames and hotbed lids. Small, low, and easy to cover in a hailstorm. Acrylic is light, very clear, and won't yellow. Use 1/8 in. for small framed lids and 3/16 or 1/4 in. for larger ones.
Windows and viewing panels in a polycarbonate or wood greenhouse, where you want to see out clearly.
Doors and vertical walls on the sheltered side, where hail and impacts are less of a concern.
Propagation covers, seed-starting domes, and grow cabinets indoors, where clarity and easy cleaning matter.
Replacement panes for old glass greenhouses, where shatter resistance and half the weight are big upgrades. Check how the frame holds the pane first, and see the clearance advice below.

The same thinking applies to chicken coop windows and shed windows: clear acrylic is a great small-window material.

Do plants need UV, and does acrylic block it?

Plants grow mainly on visible light, roughly 400 to 700 nm, which clear acrylic transmits at about 92%. Acrylite's data shows standard clear sheet passes very little UV below about 345 nm, with transmission rising through the UVA range up to about 395 nm. Acrylite adds that plants grow as well under its sheet as under glass. UV-filtering grades (Acrylite OP-3, for example) block about 99.7% of UV up to 390 nm and aren't what you want here. More in does acrylic block UV.

Some UV affects plant color, flavor compounds, and compactness, and pollinating insects use it, so some growers want it. For that, makers sell UV-transmitting acrylic: Acrylite Alltop UV Transmitting multi-skin passes the full spectrum including UV, and Röhm makes Plexiglas XT 0A370 for conservatories. For a typical home greenhouse, ordinary clear acrylic or polycarbonate grows plants fine.

How do you mount acrylic panels on a greenhouse?

Greenhouses swing hard in temperature: freezing at night, hot in afternoon sun. Acrylic moves about 0.00004 in. per inch per °F, so a 48 in. panel changes by about 0.2 in. over a 100 °F swing.

Don't point-fasten big panels. Acrylite says to install sheets 4 × 4 ft or larger in frames, not with screws or bolts. Big panels need a glazing system that lets them slide, such as aluminum bar-and-cap with EPDM gaskets.
For small flat panels with screws, oversize the holes. Acrylite's corrugated-sheet guide drills 1/2 to 5/8 in. holes for 1/4 in. fasteners, with gasketed washers tightened to snug. Use the thermal expansion calculator for clearance.
Leave gaps in channels. Acrylite's glazing guide calls for 1/16 in. clearance on openings up to 36 in., 1/8 in. from 36 to 65 in., and 3/16 in. from 65 to 90 in.
Pitch roofs so water runs off. Acrylite's corrugated-sheet guide calls for a roof pitch of at least 1 in. per 12 in. of run.
Use acrylic-compatible sealants. Acrylite's roofing guide recommends DOWSIL 795 and GE SilPruf SCS2000 silicones. Avoid sealants and gaskets that contain plasticizers, which can craze acrylic (what is crazing).

See acrylic thermal expansion for the full explanation.

How do you clean greenhouse acrylic?

Use mild soap and lukewarm water and a soft cloth. No glass-cleaner sprays, acetone, or strong alcohol, and no garden sprays that contain solvents (how to clean acrylic). Keep pesticide and fertilizer mist off the panels and rinse them if they get hit. Condensation drips are normal on any glazing; Plexiglas Alltop has a coating on both faces that spreads water into a film so it runs off rather than dripping.

We cut acrylic panels and cold frame lids to size and drill the mounting holes. Get a price in the instant quote.

Questions

What thickness acrylic for a cold frame lid?

1/8 in. works for small lids up to about 2 ft across with a supporting frame; 3/16 or 1/4 in. is stiffer for larger lids and windy spots.

Can a greenhouse get hot enough to warp acrylic?

Rarely. Air in a closed greenhouse can pass 120 °F, while Acrylite rates extruded sheet for 160 °F continuous and cast for 180 °F. Dark tints, dark-painted frames, and panels touching a heater run hotter, so vent the greenhouse and keep heaters away from the glazing.

Will hail break acrylic greenhouse panels?

Small hail usually won't. Large hail can crack flat acrylic, especially on roofs. In hail-prone areas, use polycarbonate or a high-impact multi-skin acrylic with a hail warranty overhead, and save flat acrylic for walls and small windows.

Does polycarbonate yellow faster than acrylic in a greenhouse?

Generally, yes. Polycarbonate depends on a UV-protective surface layer, while acrylic is inherently UV-stable. That's why acrylic makers offer 30-year non-yellowing warranties and polycarbonate panels typically carry 10-year warranties.

Acrylic greenhouse panels: when they make sense