That’s such a great question! The short answer is: non-washed denim fabric and you really don’t have to. If I left it at that, this would be a very short and very boring article. So I’ll assume that you are here to learn and that you really want to care. Thank you for indulging me.
Let’s start with what makes denim, well, denim. I’m not going to get super technical, because frankly, I’d just be copying from some of the other great articles that have taught me. Folks like Heddles and @Denimhound have taught me the ropes, and if you are interested in more than the basics of the fabric, I really do suggest looking into their already beautifully written pieces.
Denim is a woven fabric consisting of two directions of sturdy cotton weave, the warp and the weft. When talking blue jeans, the weft remains white and passes under the indigo dyed warp threads. What makes each individual material unique, is the pattern and method in which the weft and warp threads are woven. When talking other colored denim… well, you get the idea. No matter the color of the threads, think of the weft as the bottom or inside of the jeans, and the warp as the top or outside.
Denim material is most often categorized by weight. Weight of fabric is determined by weighing one square yard of the finished woven material. There are all kinds of weights; from some of the lightest (mostly women's stretch denim) 8oz, to the heaviest 32oz.
Let’s get to the nitty-gritty folks! What makes raw denim raw? Simply that it hasn’t touched water. It’s that simple. Raw denim is denim in its most natural state. It also comes in two states of being beyond that, sanforized and un-sanforized. The cotton yarn of sanforized denim has been steamed to pre-shrink the yarn before it’s woven in order to eliminate shrink when you *eventually* wash them. Un-Sanforized has not been pre-shrunk or treated in anyway and will shrink when they touch water (think Levis 501 Shrink-to-fit).
If you’re in need of a some stretch in your jeans, and I don’t blame you although I will eventually try to convince you that 100% cotton jeans are the master jean, then consider how much stretch you want for the fit you are trying to obtain. 1% provides enough stretch to give some flexibility without being too body-hugging. 2% will form to your body and be much more fitted. 3-4% stretch jeans are VERY form fitting and are often give moderate body contouring.
All of this information won’t do much for you trying to buy a pair of jeans unless you also consider the construction, fit, and placement of all the parts of the jeans. The best thing I can tell you is to first find a pair that you really love as a basis for measurements going forward. Once you dive in to the denim world, your wants, needs, and requirements for fit are likely to change, I know mine sure did, but starting with your current favorite pair is perfect.
What I find most important for fit is rise, waist, thigh, hip, and leg opening measurements. This is going to insure that the pants even fit your body! So duh, most important for sure! Also to consider knee width measurement (too wide would look baggy, too narrow and you now stand forever) and my personal most important, back pocket size and placement. Pocket placement can seriously make or break a pair for me. I tend to mostly wear jeans made for men, so I am very conscious of making sure I don’t look like I’m wearing a diaper underneath my jeans!
My biggest suggestion for getting into raw denim is take chances! If you can get into a store in person, do that. Go in and ask questions and try things on. You may be surprised at what you like and what fits you. If you can’t go in person, get real up close and personal with your measurements, and find a store that has a good return policy!
I believe in you all! Happy shopping and I hope you learned anything at all.