I often debate that with myself, Teacher. My wool and fleece jackets weigh aprox. the same. The fleece is cozier but the wool warmer. Wool maintains warmth when wet but fleece dries very quickly.

I most often wear a fleece jacket, down or polyfil vest, and gortex jacket when I hike in the fall. Wool seemed like a wise choice for another layer when hypothermia is a threat.