I just built a polytunnel with pvc pipes and special greenhouse film. This film has an inside and an outside.

I'm pretty sure the text on the film that says 'inside' was facing the correct way when I installed it, however, I'm now second guessing myself and wondering if there is an easy way to tell inside from outside by looking at the plastic (at a glance the plastic looks similar on both sides)? The text saying 'inside' is now buried somewhere in the soil so I can't reference that easily.

Also what are the likely effects of putting the film on the wrong way around?

Poly tunnel

  • You should be able to go straight to the manufacturer of this plastic. Is it Sun Master? What a lovely little greenhouse! I am glad you made beds instead of using pots! Great use of space! I'd probably cut back more of your surrounding vegetation to allow more light. Looks like you oriented your greenhouse correctly with south on the left side of this picture? Where do you live, what zone and what are your winters like? Does your plastic have any labeling, writing? I've had dozens of polytunnels using all kinds of plastic and I've never run into 'this side up' material!
    – stormy
    Oct 3, 2016 at 20:15
  • Do you have any material left with the writing? I just read that you buried the edges, so I get that. Is there a difference you can see between the two sides? (one side slick the other powdery for instance)? Really need a manufacturer's name...someone else here on this site might be more familiar with the specific brand you've used. Really, very nicely done! For your little walkway in front of the door, why did you use big chunks of rip rap mixed with the smaller crushed gravel? I run around barefoot and I notice stuff like that, grins!
    – stormy
    Oct 3, 2016 at 20:21
  • I live in Cape Town, South Africa. I think it's a USGS zone 7 or 8 (probably similar to drier parts of California), Mediterranean climate. The orientation is north on the left and south on the right. The garden has lots of sand stone so I used that on the path, I guess my feet might hurt when I'm barefoot ;)
    – stemie
    Oct 4, 2016 at 8:42
  • Oh and I meant to say I generally don't walk barefoot in the garden as it's quite common to see Puff Adders.
    – stemie
    Oct 4, 2016 at 8:56
  • Oh, well then...I'd be wearing tall thick boots! Those dudes are poisonous huh! My son is a herpetologist in a major way...30 probably 40 constrictors and poisonous snakes. He has a separate nursery for rats. Wait...North on the left, south on the right? Still proper orientation but poo, I was wrong looking at the shadows. You don't have to eradicate those plants around this space but I would thin. Lovely trunks. Will give you more air flow and more light. I am considered weird by friends because I am barefoot all of the time, even in the snow. Not with snakes around!
    – stormy
    Oct 4, 2016 at 20:37

1 Answer 1


It depends somewhat on "WHAT" the inside/outside properties are.

If they include an "anti-drip" or AD coating, that should be on the inside, and you might be able to see that water beads up less and runs off more easily on that side of the plastic if you spray a bit on from a plant mister.

The main problem (AIUII) with having it inside out is that the UV coating would be on the wrong side of the plastic, and that would reduce the lifetime of the plastic due to UV-aging. You would also get less or no benefit from the AD and or IR coatings that should be on the inside.

Depending on how long it's been buried you may no longer be able to find the inside markings, as those are often done with a paint that will eventually wash off.

  • I spoke to a salesmen where I bought it. It's anti drip on the inside and anti dust on the outside. As you mentioned, with the anti drip I can "see that water beads up less and runs off more easily on that side of the plastic". Apparently it's not a train smash, in terms of inhibiting plant growth. I hope I got it right though, next time I'll pay more attention. At least it's a small tunnel.
    – stemie
    Oct 4, 2016 at 8:47
  • Anti condensation more than 'drip'. Cool. Stemie WHAT is this plastic covering called, who makes it? I am very into the different plastics these days and would love to read up on this stuff!
    – stormy
    Oct 5, 2016 at 20:47
  • But do you have it arranged correctly? UV will decimate unprotected plastic within a year! Or less.
    – stormy
    Oct 5, 2016 at 20:48
  • I would ask for a tiny chunk to be sent to me so I could definitely tell whether it is inside out or right side right? Anyway, this must be expensive stuff? What did it cost? What is the name of this brand!!???
    – stormy
    Oct 5, 2016 at 20:50
  • IME it's not overly expensive - I think I paid a penny more per square foot for AD/IR, or roughly a 9% increment over the base-cost 4-year plastic film.
    – Ecnerwal
    Oct 6, 2016 at 13:26

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