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They normally have spray foam on the inside.
It is in Texas. Saw it on a Barnwood Builders show about their place in Rond Top, Texas.
Rond s/b Round
The steel in the corrugated silos is less than 1/8" thick. The edge of the door jamb is at least a five inches, indicating the walls are almost that thick as well, meaning their is some sort of insulation. Probably at least R13. If it's the spray foam as mentioned it could be as high as R30.