A contraceptive cap or diaphragm is a circular dome made of thin, soft latex (rubber) or silicone. Caps are smaller than diaphragms, but they work in the same way.
They are inserted into the vagina before sex and cover the cervix to create a physical barrier to sperm entering the womb. They need to be used with a spermicide – spermicide contains a chemical that kills sperm.
If you do decide to use a cap or diaphragm for contraception, remember they offer almost no protection against sexually transmitted infections.
If used correctly with spermicide, caps and diaphragms are 92-96% effective. This means that between 4 and 8 women out of every 100 who use a cap or diaphragm as contraception will become pregnant in a year.
You may need to practice at home to get it in place properly and they may take some time getting used to, but don't worry the clinician who fits it will help you learn how to put it in correctly.
They are put in before sex and must remain in place for at least 6 hours afterwards. After that they are removed and washed and can be reused. They offer no protection when they are not in place.