“Mono” base styles are constructed with more than one material (such as a monofilament or lace base with a poly perimeter) to allow for versatility for certain applications, such as durability, covering growing hair, etc. Breathable and strong, monofilament material is the most durable base. It can carry a large density of hair and usually be constructed with skin around the perimeter, and even with a lace front. It's a good choice if you are looking for a balance of durability and natural appearance.