Vaseline Pure Petroleum Jelly. Vaseline Pure Petroleum Jelly serves two functions. First it helps keep the outside world out - it protects skin from the effects of weather and exposure. Second, it acts like a sealant to help keep the inside world in - it forms an occlusive barrier to the natural water loss of our skin. So skin that is dry and chapped is protected from drying elements, enabling skin-softening moisture to build up naturally from within the skin.