If it's made of 100% cotton, then it will not. However, a cotton and polyester blend trench coat will give you some protection but not in a heavy downpour and not for a long time. Men trench coats made of Gore-tex, SympaTex, or other synthetic fabrics, will give enough protection from rain, but still won't be as waterproof as new garments since the waterproof qualities deteriorate over time.