How to choose film for a polytunnel
For a tunnel that will stand for several seasons, choose UV-stabilised polyethylene film about 150–200 µm thick. The University of Connecticut guide states that multi-year greenhouse film is 6 mil (about 150 µm) thick and carries a manufacturer's warranty of 4 years or more, while cheap film without this rating lasts one season. Next you choose between clear and light-diffusing film, and additives such as anti-condensate.
The film is the only part of a tunnel that is replaced regularly. The choice of film determines how much light the plants get, how quickly the film ages and how often it will have to come off. Below we describe the specifications worth checking before you buy.
Film thickness
Tunnels use polyethylene (PE) film. Thickness is given in micrometres (µm), or in English-language sources in mils (1 mil = 25.4 µm).
The University of Connecticut guide distinguishes two groups:
- cheap seasonal film (co-poly) – made in 3, 4 and 6 mil, i.e. about 76, 102 and 152 µm; it lasts one season, and the thinner grades are used on narrow, seasonal tunnels,
- greenhouse film – only in 6 mil (about 152 µm), intended for multi-year use; it costs roughly twice as much as seasonal film.
We cover our tunnels with 150–200 µm film.
UV stabilisation
Film is damaged mainly by sunlight and heat. Greenhouse film contains a UV stabiliser that slows this process. According to the University of Connecticut, such film carries a manufacturer’s warranty of 4 years or more.
The same guide lists what shortens the life of the film:
- crop protection products and chemicals from pressure-treated timber,
- the film heating up where it touches the structure (hoops, purlins, fixing profiles).
So when buying, ask not only about thickness but also about the stated number of seasons and the warranty terms. We give a 3-year warranty on the film on our tunnels.
Clear or light-diffusing film
Diffused (light-diffusing) film changes the direction of part of the sunlight. According to the University of Connecticut, this has several effects:
- less scorching of plants,
- more light reaches the lower leaves, which matters especially in tall crops,
- less favourable conditions for fungal spores and insects to develop.
The same guide gives PAR light transmission (the range used in photosynthesis): 88–91% for UV-stabilised film and 77–88% for film with IR and anti-condensate additives and with diffusion. So additives come at a cost in the amount of light.
Film additives
| Additive | What it does | What UConn says |
|---|---|---|
| UV stabiliser | slows the ageing of film in the sun | the basis of multi-year film |
| anti-condensate (AC, anti-drip) | water condenses into a thin layer and runs off instead of dripping | usually works for several years; droplets reduce light and encourage disease |
| IR (thermal) | keeps radiant heat inside | 10–20% savings in heated greenhouses |
| diffusing | scatters light | less scorching, more light on the lower part of the plants |
The guide also links IR film to faster plant development, probably thanks to higher tissue temperature at night.
Single or double (inflated) film
These are two different systems, not two thicknesses of the same film.
Single film is one layer stretched over the hoops. This is how we cover all our tunnels, single and multibay.
Inflated double film is two layers with a blower pushing air between them. According to the University of Connecticut, this air cushion reduces night-time heat loss by about 40%. It needs the blower running continuously (the guide recommends a pressure of about ¼ inch of water column, slightly more in wind and snow), and therefore a power supply in the field.
| Feature | Single film | Inflated double film |
|---|---|---|
| Layers | 1 | 2 with an air cushion |
| Heat loss at night | baseline | about 40% lower (UConn) |
| Blower and power | not needed | needed all the time |
| In our range | yes | no |
We do not make tunnels with double film.
White and green film on garden tunnels
Ready-made garden tunnels come with milky (white) and green film. This is a different segment from tunnels for commercial plantations.
Installation affects film life
The life of the film also depends on how it behaves on the structure. The Cornell University guide calls wind the greatest enemy of a high tunnel and recommends closing the sides and end walls in strong wind. The University of Connecticut points to the film heating up where it touches the structure.
The most common mistakes when choosing film
- Seasonal film on a multi-year tunnel. Cheap co-poly film costs less, but according to the University of Connecticut it lasts one season. On a tunnel meant to stand for several years, that means taking off old film and pulling on new film more often.
- Comparing only the price per metre. Two films of the same thickness can differ in UV stabilisation, additives and warranty.
- Ignoring condensation. Droplets on the film reduce the amount of light and encourage disease when they drip onto plants (UConn).
Checklist before you buy
- Thickness in µm – for multi-year use about 150 µm or more.
- UV stabilisation and the stated number of seasons.
- Clear or diffusing – depending on the crop and the amount of sun.
- Anti-condensate additive, if water often condenses in the tunnel.
- Warranty terms for the film.
We choose the film together with the structure during a visit to the customer. Start with the configurator or call us: +48 512 208 808.
Sources
- Plastic Film Update — J. W. Bartok Jr., University of Connecticut, UConn IPM (updated 2013) (accessed 11 October 2026)
- Structures — Cornell High Tunnels (Cornell University) (accessed 11 October 2026)