Alva Baby Birth to potty nappies are an efficient and easy to use nappy, so much so they have become the best loved brand for economical reusable nappies. You can opt to have yours come with an absorbent 3-layer bamboo insert which stuffs inside the pocket. Additional boosters can be added for extra absorbency. The outer layer of the nappy is a waterproof and breathable TPU. The inner layer of the nappy is a polyester suede cloth (100% man-made, not derived from animals) which helps to draw moisture away from your baby's bottom and in to the insert.