One of the world's oldest known fibers, silk is a natural protein fiber made by silk worms (yep, these are actually caterpillars). The highest quality and most expensive silk is Mulberry silk (which get its name from the all mulberry leaf diet the silk worms eat), and is produced by the Bombyx Mori moth during its caterpillar state. Mulberry silk threads are rounder, smoother, and have a lighter more uniform color than other types of silk. Silk comes in many different textures and is great for both warm and cool climates. And despite silk's delicate appearance, it's very durable and can last a long time if cared for properly. Sunlight, humidity, and heat can actually damage silk garments so it's best to store them in breathable garment bags in cool dim places.