The structure of our waterproof products is such that rain is prevented from passing through by coating the back surface of the fabric with water-resistant material. Furthermore, water-resistant tape on the back of seams stops absorption of water. (Some welder products do not need this feature.) The official term for water-resistance is water pressure resistance.
*Waterproof materials prevent water from penetrating clothing, but since the inside of the clothes does not breathe well, it gets humid and steamy as you sweat.