The Medela Therashells are designed to provide mothers relief between feedings. The large opening backs help soothe sore nipples and protect from further irritation, while the small opening back help with flat/inverted nipples or engorgement.Includes: 2 shells. 2 flat/inverted nipple shellbacks (small opening). 2 sore nipple shellbacks (large opening). 1 instruction manual.. Helps solve common problems faced by breastfeeding mothers. Natural round shape is designed to be discreet under clothing and help keep nipples dry and prevent irritation. Soft flexible backs keep nipples dry and prevent further irritation. BPA free.