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Old September 3, 2016   #17
Cole_Robbie
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Join Date: Jun 2012
Location: Illinois, zone 6
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Most poly is 6mm. It is surprisingly strong. A pressure washer will not damage it. Not that you have to worry about snow, but a single layer of 6mm was enough to collapse my high tunnel from snow, without tearing the plastic first. It pulled five 4x4 posts set in concrete, at each end, about two feet at the top. The force required was enormous. My other greenhouse held, by my guess, over 2,000 pounds of snow and ice on the plastic with no damage.

If you use double-layer poly, you'll need an inflation blower. Use outside air to inflate. Also, if you have roll-up sides, use a single layer for that part, not a double, because it can't be inflated. Without inflation, the layers of plastic rub together and turn cloudy very quickly.

The newer plastic has an "infrared block" quality to it. It is opaque, not clear. It is a lot better about not getting too hot in full sun. Clear plastic will make a solar cooker in the late spring and summer.
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