How to choose the best commercial polytunnel covers: thickness, UV protection and light diffusion
Water drips onto your seed trays, but above the hoop the plastic has rubbed thin. Two faults, two causes. Comparing replacement polytunnel covers by thickness alone leaves the condensation problem untouched.
Underneath, winter lettuce has little daylight to spare. Tomatoes shade their own lower leaves. Summer-only growing and wind exposure change the demands again; a micron figure says nothing about light reaching the crop or warmth escaping overnight.
What thickness do commercial polytunnel covers need?
Your quote says 720 gauge; another says 180 micron. Same thickness, 0.18mm, and a common commercial specification. At 600 gauge, you're buying 150 micron film. Going to 200 micron adds plastic, without telling you how readily it tears.
At a rough fixing, a loose sheet rubs in the same spot. Another 20 microns won't remove the cause. Two sheets of equal thickness still need comparing for polymer quality and tear resistance.
Wind catches a damaged edge. Does the tear stop or travel? For exposed-site polytunnel covers, the tear-resistance figures matter alongside thickness. The fixing requirements must also suit your rails: extra material leaves loose anchors loose and rough metal rubbing. Frame protection and tension remain part of the job.
Does UV protection stop sunlight reaching crops?
No. “UV stabilised” describes protection for the plastic itself, which sunlight degrades. It doesn't answer the separate question of how much ultraviolet light reaches your plants.
Crop colour and pollinating insects make that distinction more than wording on a quote. With UV-resistant polytunnel covers, “UV protected” leaves you without the light characteristics. Is it UV-open or UV-blocking? The answer needs to fit both your crop and your pollination system.
A quote for 180 micron film might put a five-year UV degradation warranty beside an expected life of eight to ten years. Only the first is warranty cover. Nor does protection against sunlight degradation mean cover for a storm tear or a hole worn against a hoop.
Nobody can promise the replacement date for your particular tunnel.
Clear or diffused polythene greenhouse film?
Afternoon sun lights the tops of your mature tomatoes. Below them, leaves shade leaves. Diffused polythene greenhouse film scatters incoming light, sending it into that canopy from different angles. More light arrives directly through clear film; those descriptions alone don't settle which commercial polytunnel covers suit the crop.
Does a milky appearance mean less growing light? Not necessarily. One commercial film gives figures of 89% light transmission and 95% diffusion. The first measures light entering; the second describes its scattering. Diffusion isn't another word for shade.
For winter salads, daylight is already limited. A dense summer canopy presents a different problem: getting light beyond its upper leaves. Put transmission figures beside each other only when they've been measured on the same basis. Looking at the sheet's colour won't answer either question.
What do thermal and anti-drip films do?
The sun goes down; warmth stored in your beds starts escaping as long-wave infrared radiation. A thermal additive slows some of that loss through the roof. Will it keep frost out? No. An unheated tunnel remains exposed to frost.
By morning, droplets have gathered above the seedlings. With anti-drip treatment, condensation spreads across the film rather than collecting into drops.
“Thermal” on the order doesn't tell you whether polytunnel covers have anti-drip treatment. You need each property specified, and ventilation still has a job to do. Before fitting, establish which face goes inside and how long the anti-drip effect lasts. A five-year UV warranty doesn't give you five years of anti-drip performance.
What do replacement covers cost, and should you pay for fitting?
A running-metre price needs a roll width beside it. For the bill you'll pay, get VAT and delivery included in the complete sheet price.
One supplier's listed starting price for diffused film is £20.22 per running metre, including VAT. Twenty metres at that rate comes to £404.40, with delivery and fitting still to add. Wider options change the price.
For covers, measure over the hoops and allow for the specified fixing method. Ground width multiplied by tunnel length won't give you the sheet size.
Doing the fitting yourself means finding enough people to handle the sheet in calm weather, with suitable access and a sound frame. Set aside a working day for a straightforward replacement; repairs take longer. Fitters free up your team, with labour and travel added to the bill. We can't price that without dimensions and fixing details.
Still intact? Keeping it costs nothing today. Compatible repair tape deals with an isolated puncture. Plastic turning brittle across the sheet calls for replacement.
What to check before ordering
Today, measure the tunnel and photograph its fixings. Use those details to obtain two crop-matched specifications for polytunnel covers, each stating light transmission, warranty exclusions and a complete sheet price.
You can get in touch with us to discuss the two specifications.
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