Fleece is a human-made synthetic material, and wool is a natural fiber derived from animals. Fleece retains body heat, is breathable and moisture-wicking, and dries fairly quickly. Certain designs are made to be wind- and water-resistant. Generally, fleece doesn’t repel smelly odors.
In comparison, wool regulates body temperature well — even when wet — and boasts anti-odor properties. It’s also naturally water-repellent due to lanolin that coats the fibers, though it takes longer to completely dry compared to fleece.