To understand Crepe and how it is made, we have to dig a little bit in to spinning techniques. Only a little bit. I'll try and keep it brief.
Fibers, or in the case of silk filaments, are spun in to threads before weaving. Fibers/filaments are spun with either a z-twist or an s-twist. A Z-Twist means that when the fibers are spun, the spirals formed from spinning conform to the central portion of the letter z. S-Twist means that the fibers when spun conform to the central portion of the letter s (Fairchild, p. 184).
With that bit of technicality out of the way, we can jump in to crepe. From All About Silk, crepe has finer warp threads with heavier filling threads, with threads alternating between z and s twists. These irregularities give crepe a crinkly, pebbly texture, and an elegant drape and flow. However, the irregularity of the texture makes it hard to hold a crease. Among the easier fabrics to work with BECAUSE of it's texture, crepe truly is a dream drape to work with.
One additional word of caution before buying or working with crepe: due to how very tightly twisted the filaments are, crepe is VERY prone to shrinking when washed. 100% silk will dye to any color you want, and despite belief to the contrary, silk CAN be washed with water, it can even be machine washed. Now, having said that, there I am including the caveat that we have not personally experimented with washing silk crepe and as always advise testing any pre-treatment on a small sample to make sure the results are to your liking. With all that, be aware that due to the extra twists to the threads during manufacture, crepe will definitely shrink, so make sure to purchase extra to allow for that shrinkage.