Bags used to keep pizza hot while being transported are commonly referred to as hotbags or hot bags. Hotbags are thermal bags, typically made of vinyl, nylon, or Cordura, that passively retain heat. Material choice affects cost, durability, and condensation. Heated bags supply added heat through insertion of externally heated disks, electrical heating elements, or pellets heated by induction from electrically generated magnetic waves. Innovations in delivery bag designs have allowed without the usage of a fixed box for bike delivery, such as a hard frame, back straps, and waterproofing. These systems proved to be cheaper, more efficient and faster to use.