This is what we call a denim that is “loomstate”, that is to say that it has not been treated or altered in any way post weave. Raw denim is less stable than sanforized denim and will shrink when washed. Many denim aficionados prefer to buy raw denim garments, created from denim in its pure, untreated state and are happy to deal with the vagaries and uncertainties of shrinkage. If you prefer to “play safe” you should purchase jeans where the denim has been sanforized, or at least one-washed.