The Mountain Laurel Designs Cuben Packing Cube is an ultralight stuff sack made from 3.3 oz Dyneema Composite Fabric (DCF), sold in three sizes: 10 g (S), 14 g (M), and 37 g (L). DCF is inherently waterproof rather than coated, so the fabric itself won't wet out the way treated nylon can over time, though the item is listed as not fully submersible — the zipper, not the fabric, is the limiting factor.
Closure is a YKK zipper with dual pull tabs for easy one-handed access from either direction, a small but useful detail when digging through a stuffed pack. As a single-compartment cube rather than a compression sack, it's built for organization — keeping clothing, food, or electronics separated and easy to find — rather than squeezing volume out of bulky items.
At these weights it barely registers even in the largest size, making it a reasonable addition for ultralight hikers who still want internal organization, and useful for anyone who wants water-resistant separation between items in their pack.