Fleeces

Fleece weight is quoted in gsm and the useful range for work is roughly 200gsm for a mid layer you wear under a jacket, up to 350gsm and above for a fleece worn as the outer layer. Heavier is warmer and slower to dry.

No. Fleece is warm when damp and dries quickly, which is not the same thing. If you need to keep rain out, put a jacket rated to EN 343 over it. Some of the hi vis fleece jackets here carry a rain patch across the shoulders, which helps in a shower and is still not a waterproof.