Building a sauna in a shed, Sauna foil???

[Jensa1]

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Hi!

I'm building a 15 sqm "friggebod" with half as a sauna and the other half as a regular room.
Now the question is, SHOULD I have sauna foil or not, and should I have building foil or not?
I will maintain a temperature of just above freezing when we're not using the sauna!​