One size fits all. Works on all hair types. For women, teens, girls, athletes of all ages. 2 packs. 20 pieces total. There are 10 pieces per pack. 2 packs included for a total of 20 Silkies. They come in a zippered pouch for convenience and storage. They are coated so that they will not tear the hair. Silkies last 10 times longer than traditional rubber bands because they are not UV or heat sensitive. They do not become brittle and break like rubber bands. Mia Silkies are hair elastics made out of durable silicone material.