Glass has been the standard for greenhouse glazing for well over a century, and for good reason. It’s clear, it’s durable and plants thrive under it. But if you’ve ever had to replace a broken greenhouse pane, deal with an ageing aluminium frame that can’t take the weight of thick glass, or simply tried to move a full sheet of horticultural glass without cracking it, you’ll understand why more gardeners and growers are switching to acrylic.
Clear acrylic transmits around 92% of visible light, which actually edges out standard horticultural glass at roughly 90%. Your plants won’t notice any difference. What they will benefit from is better insulation, since acrylic’s lower thermal conductivity means the greenhouse holds heat more effectively on cold nights.
Which Thickness for a Greenhouse?
For standard hobby greenhouses with aluminium frames, 2mm or 3mm clear acrylic fits most applications. These thicknesses slot into the same glazing channels as the original glass and weigh significantly less, which puts less stress on older frames. 2mm is the budget-friendly choice and works well for sheltered positions. 3mm adds a bit more rigidity and impact resistance, which is worth it if your greenhouse is exposed to wind or sits near where children play.
Larger commercial or timber-framed greenhouses may benefit from 4mm acrylic, particularly for roof panels where hail or falling branches are a concern. Beyond 4mm is overkill for greenhouse glazing. You’d be adding cost and weight without meaningful benefit.
Acrylic vs Glass for Greenhouses
The practical advantages stack up quickly. Acrylic weighs about half as much as glass, so you can handle full panels on your own without worrying about dropping and smashing them. If a panel does take a heavy impact, acrylic is roughly 17 times more impact-resistant than standard glass. It won’t shatter into dangerous shards, which matters when you’re working in a space surrounded by the stuff.
UV stability is built into quality acrylic sheet. It won’t yellow, become brittle or lose clarity over time the way some cheaper plastic alternatives do. You can expect at least 10 years of clear, trouble-free performance from a decent acrylic panel, often considerably longer.
The one area glass holds an advantage is scratch resistance. Acrylic will pick up surface scratches if you’re careless, but in a greenhouse setting where nobody is polishing the panels to display-cabinet standards, this rarely matters. Light scratches don’t affect light transmission in any meaningful way.
Replacing Broken Panes
This is where acrylic really earns its keep. Measure the opening in your greenhouse frame, taking the width and height in millimetres. Older greenhouses often have slightly different sized openings, so measure each one individually rather than assuming they’re all the same. Order your acrylic panels cut to size and they’ll arrive ready to fit.
Most aluminium greenhouses use glazing clips to hold the panels in place. Slide the new acrylic sheet into the channel, click the clips on and you’re done. The whole job takes a few minutes per panel. For putty-glazed timber frames, bed the acrylic in the same way you would glass, using a flexible glazing sealant rather than traditional linseed putty, which can react with acrylic.
Cutting Panels to Fit
If you need to trim a panel on site, acrylic is far easier to cut than glass. For straight cuts on 2mm or 3mm sheet, a sharp Stanley knife and a straight edge works perfectly. Score the line firmly several times, then snap along the score. Thicker sheets need a fine-toothed saw.