The important part is to store them in an airtight container. I vacuum pack them in the food storage bags that came with my vacuum packer for food. The reason that plastics, vinyl & rubber, etc. become hard & crack is the loss of the lower molecular weight compounds in the mixture. Plastics are formulated to the desired flexability by combining higher molecular wt. ingredients with lower mol. wt ones. When the lower mol. wt. compounds evaporate, the stiffer high mol. wt. materials are left. Thus, you have less flexibility & more brittleness. Heat accelerates this process. Sealing the gloves in an airtight container retards it. This won't preserve your gloves indefinatly. Compounds with complex molecular formulas can decompose into simpler compounds regardless of storage conditions. Inorganic compounds such as water or salt are too simple to decompose. For more info, lookup plasticizers in the Wikipedia.