What is the main purpose of the foam inside a self-inflating mat?
All self-inflating mats I have seen are self-inflating in the sense that you’re supposed to inflate them yourself. [That is, the mat self-inflates a bit, but mostly you have to breathe the air in.]
Given this, what purpose does the foam inside the mat serve? If there was none, wouldn’t the mat be lighter?
My hypothesis is that the foam prevents the air from moving inside the mat, thus greatly increasing the heat resistance. Is that the case? (Do you have some dependable sources?)
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I have a self-inflating mat, and I think the foam serves three purposes. In order of importance:
- It sets the shape of the mat when inflated. Think of the foam as limiting how far the opposite walls of the mat can be in any one place. If you didn't have this, the mat would become more of a circular tube as it is inflated. For cushioning, the foam does little compared to the air pressure.
- It increases the insulation value of the air inside the mat, as you say, since it keeps the air from easily circulating. Note that these mats are warmer than just inflatable mattresses.
- It provides for some self-inflation. Actually I think this is merely a mildly useful by-product of having the foam there for the other reasons, but if you're selling these mats you might as well feature this. I find that my mat self-inflates most of the way, but I still have to blow into it for the right pressure. When you blow into it, you get moisture from your breath in there, which can't be good from a standpoint of mold growth and the like. Letting is self-inflate to the extent it can minimizes this.
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The foam inside the mat prevents heat loss through convection which would be the case with the air if there was nothing to prevent it moving. This forms part of the open cell vs closed cell argument for sleeping mats.
This post was sourced from https://outdoors.stackexchange.com/a/4760. It is licensed under CC BY-SA 3.0.
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