Barrier methods of birth control typically include the condom, diaphragm, cervical cap, and contraceptive sponge. These options provide a barrier to sperm, preventing pregnancy by effectively forming a block to any sperm passage. They must be used every single time you have intercourse. Only the condom will effectively prevent pregnancy and transmission of STDs (except if an STD is present on skin area outside the condom barrier).
Condoms, also called rubbers, now come in a variety of scents and textures. This sheath is placed over the erect penis so that any semen ejaculated will remain in the condom. You can only use a condom one time. Condoms made from latex are considered the most effective barriers for preventing pregnancy and STD transmission (no other barrier methods effectively protect against STDs). Never use Vaseline, petroleum jelly, lotions or oils in conjunction with the condom. You can use K-Y jelly, and use of a spermicide with the condom offers even better birth control protection. Failure to prevent pregnancy is associated with not using a condom every time you have sex. If the condom breaks or slips, allowing some sperm to escape into the female's vaginal canal, a pregnancy can result.
The diaphragm is a shallow latex cup, with a spring mechanism in its rim, that holds it in place once inserted in the vaginal canal. A doctor has to examine and measure you in order to get a proper fitting diaphragm and after childbirth your size typically changes. You insert it prior to intercourse (even hours before) after applying spermicidal cream or jelly in its dome. When inserted properly it covers your entire cervix and remains in place comfortably. You can remove it a couple of hours after intercourse. Always check it for holes or tears and replace it per your doctor's recommendations. Wash it with warm soapy water after use and store it in a sealed container. You don't want to have multiple acts of intercourse with it in place for an extended period of time, or leave it in for more than 24 hours because that will increase your risk of developing a UTI (urinary tract infection) or toxic shock syndrome.
The cervical cap is also made from latex and smaller than the diaphragm. It fits just over the base of the woman's cervix. Some women find it challenging to insert and place properly because it is quite small. You have to be fitted by a doctor and fill it with spermicide before using. You can insert it up to 8 hours before sex and leave it in for up to 48 hours post intercourse. With "perfect use' its failure rate is 9%. The failure rate goes up once a woman has had children, since the shape of the cervix changes with childbirth, and a good fit (and seal) may be more difficult to achieve. Being very overweight can also make placement difficult. The cap also has a risk of toxic shock syndrome if left in too long.