A bowstring needs to be waxed periodically to prevent fraying and keep it functioning well. I like to make my own bowstring wax. Start with beeswax from your local beekeeper or online beekeeping supply house. Melt it inside a clean tin can placed into a pot of boiling water (be careful, it is flammable) and add a little pine pitch or pine rosin to the liquid wax. Stir well. The more pitch you add the stickier the wax will be.
Tape some waxed paper over one end of a toilet paper roll. Place the tube onto a paper towel in case you drip a little. Pour the warm liquid into the tube and let it cool. Trim the excess cardboard tube with a sharp knife or scissors. Apply the wax mixture liberally to the string by rubbing the open end of the tube on the string. Take a small piece of leather and rub or burnish the wax into the string. A tongue from an old, worn out pair of shoes or boots works well. By working the string between your fingers with the leather, the wax warms and works into the string and acts as a lubricant and protection from abrasion.
You can use straight beeswax, but the pitch makes the wax more flexible in cooler weather, and it smells good to boot! If you want a little softer formula, add a little lanolin to the mixture.