ANDY'S ANSWER: The purpose of the scrotal sac is to let the testes hang away from the heat of the body because they need cooler temperatures to produce sperm. If the testes are cold, the scrotal sac will wrinkle up and pull the testes closer to the body. Other things may cause the scrotum to contract and push the testes up, like sexual excitement or even exercise. When the testes are warm, like in a hot shower, the muscles of the scrotal sac will relax and the testes will drop down.