Okay, I'm not a textiles expert, but I love jeans, and here is my understanding of them. First of all, denim is a type of twill, which is what gives it the "diagonal" look to the fabric. 3x1Z is the common right hand weave, and means that a warp thread (the vertical, colored yarn is the warp yarn) goes over 3 weft (the horizontal, white yarn) threads, and under one, on the loom. The result is that the intersection moves to the right, and so on. Right hand twill (running left to right in a north easterly direction) (Z) is harder and harder wearing, because the weaving process compacts the threads composing the fabric, while left hand twill (S) (the same process, but in the opposite direction) is softer, for the opposite reason. Lighter denims can also be 2x1 - You see these in jean shirts, etc.... Ringspun refers to the method by which the yarn woven into denim, is, well, spun. Denim can be made of either ringspun yarn open-ended yarn. Honestly, I'm not sure exactly how they differ in manufacture, but ringspun yarns are stronger, but less even, thus the texture on the majority of "designer" jeans. The weight of the denim refers to the weight per square yard. I've never actually tested this. Fancy jeans like the pair of Paper Denims I have on are usually 12 ounces or so, up to about 14 ounces and down to about 10 ounces (I call those girly man jeans.) A lot of Japanese (and more recently, fancy American companies) boast "selvedge" on their jeans. The selvedge refers to the fabric at the edge of the loom. Vintage looms were considerable less wide than modern looms, which means more selvedge, and also slower production. I wear out my jeans in no time flat, and have never had to test the durability of selvedge. I've been told that the quality of the jeans depends primarily on the yarn used. A denim of similar weight of finer and better yarn dyes more easily, feels softer and more durable. For durability, I guess that you would choose the heaviest denim made from very well carded and combed, relatively fine, ringspun yarn. There are lots of other considerations, but for pure toughness, I find that heavy weight Diesel jeans take the cake by far. Okay, I hope I got that right. Shouldn't Shirtmaven and others in the business have a better understanding of this than I?