Kozy Coat style season extenders have been in use in my early garden for some time. I’ve used a couple different brands with varied success but this year I had a breakthrough.
I have been buying a few more of the red Kozy Coats each year since I first saw them. Last year I got a bit curious and I left one out. I had some cilantro that came up from seed that had fallen from a previous planting so I put a kozy coat around a bunch in late fall to try and hold on to them as long as I could. Cilantro is pretty hardy so I was able to make some extra fresh salsa with tomatoes and peppers that were harvested earlier. But the surprise came in spring time.
The cells were filled with water but kozy coats leave the top open. A little layer of something resembling algae formed on top helping to prevent evaporation of water in the cells, but still allowed the water to expand as the water froze and became ice.
You would think that all that freezing and thawing would pop the plastic but it didn’t. Also they are supposed to be stored inside when not in use to protect from the sun’s UV rays that can breakdown the plastic prematurely.
Here it is spring and my kozy coat survived being frozen for the whole winter, several hard freeze and thaws, UV rays from being outside 24 hours a day for about 8 months straight plus a couple seasons worth of use prior to that.
Obviously from this experiment there are durable kozy coats out there. I would still suggest putting them away out of the sun anytime not in use and they will last even longer. If you are really serious about their longevity you can make most outdoor plastic last a really long time by spraying it with 303 Aerospace Protectant which is a water based UV Protectant and plastic lubricator. I use it on everything plastic or rubber. Clean your kozy coats with soap and water in the fall, dry them, then spray and wipe off the 303 Aerospace protectant before you put them away for the winter and they should last for years - provided you don’t pierce a kozy coat with a rake.