Sanforization is a mechanical finishing process, named after its inventor, that compresses woven fabric before it is cut and sewn into a garment. The process controls the natural shrinkage that raw cotton fabric would otherwise undergo the first time it gets wet, so the fabric arrives at the cutting table already close to the size it will stay at.
For you as a wearer, this matters because sanforized jeans usually shrink only slightly further, commonly around 1 to 3 percent, after their first proper wash. That means the size you try on is a fairly reliable guide to how the jeans will fit once they have been washed a few times, which is why most modern jeans, including most raw denim, are sanforized.
The opposite approach, leaving the fabric unsanforized, is now a smaller niche within raw denim, chosen for a different fit and break in process. See the entry on unsanforized denim for how that compares, and our jeans size guide for general advice on choosing a starting size.
