Minecraft wiki entry for Elytra, associated text: When the durability reaches 1, elytra stop working until they are repaired, adopting a tattered texture in the inventory. The damage ends at durability 1, so they can never fully break. A pair may be repaired by either using the Mending enchantment, combining two pairs in a grindstone, or combining it in an anvil with phantom membranes. In an anvil, each piece of membrane repairs elytra by 108 durability points, requiring 4 pieces to fully repair them.