What insulation gives the best R-value ?

You don't use tyvek for insulatory reasons. You do it to stop air movement white undermines the effect of fiberglass insulation. But most importantly its is a moisture barrier that presents your house from rotting. The reason I say this, next time you look at a glass on a warm day with some cold ice tea you see ijt condensing? Well that's your house a air conditioned home without a moisuee barrier will condense water in the walls you don't want that. Plus it would be cheaper to tyvek and insulate with sheet goods(without taping, which because if the tyvek would no longer be neccesary) then to tape all your sheetgoods without the tyvek.