Silk is a fashion mainstay-particularly for formal wear. Spun from un-wound moth cocoons that dine on mulberry leaves (aka silk worms) and woven into a broad range of fabric types, silk is the original luxury fabric. Silk fibers are extremely strong, yet fine in thickness, enabling it to be both extremely wind and puncture resistant, making it the perfect base for armor and the perfect winter coat material (historically Chinese and other East Asian societies wore coats, not cloaks, for winter protection).
Silk is versatile! Yet for all its history and impact on both Asian and European history and cultures, few people understand its weights and fabric types well enough to make truly informed choices at both fabric stores and clothing stores.
Silk weight is measured in a unit called “mommes” (abbreviated mm in textile contexts) which is how many pounds a silk bolt 45 inches wide by 100 yards weigh. The smaller the number, the lighter weight the fabric. The lightest weight silk I’ve located is a 3mm silk gauze. By contrast, many silk noils (aka raw silks) will weigh between 30mm and 35mm, depending on where you buy it. That makes the silk noil 10 times heavier than the very light and sheer silk gauze. Your average crepe de chine is in the middle, ranging from 12mm to 16mm. Doupion (i) is typically around 19mm (see http://www.dharmatrading.com/html/eng/1665272-AA.shtml for actual fabrics at these weights).
Weight alone will not determine how hot or cold your silk will be to neither wear nor what sort of garments it should be used for- though it is critical to that equation. Weave is the other major consideration needed to make that determination. Weave is about how the fibers are put together-how densely and in what arrangement the threads are interlocked. Weave transcends fibers. Gauze, an open woven fabric, may be made of silk, cotton, linen, or any number of artificial fibers and/or blends. Gauze is, by its nature, at least somewhat sheer-as an open weave, the strands are not very close together. Gauze is highly sought after for veils, sheer blouses or shifts (in historic clothing), and so forth. On the other end of the spectrum are velvets (woven with a deep pile), organzas, silk noils, doupion(i), and brocades (silk brocades are typically silk-rayon blends). Weave is easily seen with the eye-if it looks densely or tightly woven, it’s probably a tight weave.
Combined, momme value and weave will provide you will a good sense of how any given silk fabric can and should be used. From crisp weaves like doupion to softer, more clingy fabrics like habotai (aka China silk) and chiffon, the combinations of weight and weave are almost endless. With a little thought and experimentation, however, you can find a silk that cool for summer, warm for winter, and everything in between.