They are about the same. If you foliar feed, overspray can build up and lessen the mylars efficiency. It's said that the creases in the blankets can cause hot spots. I've used them for years and never noticed one. If I did, I would probably aim them for better penetration

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I use them because they are cheap, opaque , allowing me to see into the space without opening, and light, allowing me to hang them with push pins. When a situation arises making it necessary to pull it, It only takes minutes and I'm only out around $8.and the walls were protected except for some pinholes to fill.