What is the R factor of dead air

I need to complete a temporary enclosure using my car port as a non permanent work shop. I have nearly complteted the task using vapor barrier plastic. Right now a single layer will keep out the blowing rain and wind. But what will two layers do, one either side of a stud wall for insulation. And will my humidity level belowered in the car port by utilizing heat generated from having light bulbs turned on? The car port will be fully enclosed.
I suspect the R value may be low and will only go high when the distance molecule of air will move is less than one eigth of an inch.
Is there an R factor to such a temporary treatment to a stud wall?

You have to figure out a way to prevent convection currents from flowing in the dead air space for it to have any value. This is actually how fiberglass bat works- the insulation properties are mostly due to the trapped air. Its hard to say what the R value will be for larger volumes, but its better than nothing.

It's figured as about R-1 for spaces of 1/2" - 4".
This presumes a perfect seal to contain the air.

Your plastic has an R value of about 0!

Foam panels are light weight and have very high R values per unit thickness. Might want to think about something like that to sheath the space.

If the space is tightly sealed think about exchanging some air to reduce the RH in the space.

I have a carpenter friend that told me a funny story about plastic sheathing and humidity.
He and some friends were on a fishing trip. The old one room cabin they stayed in was un-insulated and there was no heat.

They were cold and the wind was blowing through the cabin. So, being carpenters, one of them had the bright idea to cover the ceiling and walls with visqueen that he had in his truck. They completely covered the interior, walls, ceiling, windows, door.
He said the cabin warmed up real quick and they were able to sleep.
That was the good part.

Before dawn the interior was dripping so much moisture they thought it was raining inside. He said "..everything and I mean everything. Clothes, food, bedding, everything was so wet you'd think we were under water!" They had to leave and head back home.