My shop is a 33x30 pole barn. I used 1/2 plywood on walls and ceiling. Blew insulation in ceiling and used 4" thick ridged foam boards used on rubber roofs in the walls. Came in 4x8 sheets and found it Craigslist for $3 a sheet. View attachment 1715527531
That's a steal on those foam boards. I used foil faced foam boards on my ceiling and a foil type tape on the seams. Don't use regular duct tape, it starts to come off after awhile. The foil keeps things brighter in there too.
