Hello, 

I’m working on getting my supplies for my new home I’ll be starting anytime and had a couple of questions about wall sheathing. 

What I’m doing is framing inside of metal building and was planning on putting sheathing on the outside of the framing against the metal purlins. The walls of the metal building will already have 4in vapor barrier blanket insulation and the roof will have 6in. There would be an air gap between the the framing and purlins with the insulation roof and walls. Then the walls inside would be additionally insulated. 

Now my questions is what material sheathing I should put. I was originally planned on doing OSB but I found this product and it has me interested. 
https://schillings.com/products/lumber/plywood-sheathing/sheathing/insulated-sheathing/1%e2%80%b3-4%e2%80%b2-x-8%e2%80%b2-ox-iso-red-ci-insulation-sheathing/

This would give me a little extra R-Value and provide another radiant/vapor barrier. Would this be any benefit or a bad idea? Also should I just use on the walls or ceiling or both?

Thanks,
Jeff