There are may different types of silk yarn available.  One of the highest quality silks out there is Mulberry Silk.   This silk is only harvested from Silk worms that have been fed Mulberry leaves, which results in the the finest silks fibers in the world.  Mulberry Silk is another of the Hypoallergenic yarn options available and yarn made from this is strong and durable with a beautiful sheen and soft feel.