A cap, like a diaphragm, is a barrier method of contraception. It fits inside your vagina and prevents sperm from passing through the entrance of your womb (the cervix). Caps are soft, thin domes made of silicone, and come in different shapes and sizes.
To be effective in preventing pregnancy, a cap needs to be used in combination with spermicide, which is a chemical that kills sperm.
You only have to use a cap when you have sex, but you must leave it in for at least six hours after the last time you had sex. You can leave it in for longer than this, but do not take it out before.
When you first start using a cap, a doctor or nurse will examine you and advise on the correct size or shape. They will show you how to put in and take out the cap, and also how to use the spermicide, which must be applied every time you use a cap.
A cap provides only limited protection against STIs. If you’re at a high risk of getting an STI – for example, you or your partner has more than one sexual partner – you may be advised to use another form of contraception.