If using a condom is as easy as "pulling on a sock," why do people hesitate--at the moment of truth--to slip one on? Some men worry that their erection, much like the date on the condom wrapper, will expire. Perhaps because it won't fit them well. But condoms come in different lengths, widths, and thickness, and many men actually say they stay hard longer when they use condoms. All the more reason to treat condom shopping like a quest for jeans: the more you try, the better your chances of scoring the perfect fit.

"Condom manufacturers don't put size on a label, so it takes some playing around," says Jon Knowles, director of public information for the Planned Parenthood Federation of America. And speaking of playing around, foreplay and condom use go hand in hand for some couples. Many couples say using condoms lets them focus more on pleasure and less on infection and unintended pregnancy.

As a contraceptive, condoms have a 14% failure rate in "typical use," which makes them superior to diaphragms, cervical caps, and several other methods. For the condom's "perfect user"-- someone who doesn't puncture its surface, rub Vaseline on its exterior, re-use it post-ejaculation, or try other Olympic feats--the failure rate is only 3% (not quite as good as the Pill, but close). Equally important, condoms are considered the best available form of protection against HIV and several other sexually transmitted infections (STIs). Condoms are inexpensive and easy to get; they are discreet and disposable; and they do not require a prescription. There are so many varieties of colored, ribbed, lubricated, extra-thin, tinted, and studded "rubbers" that you might read some basics below before you take your research into the bedroom lab.

Plastic condoms are coming down the pike

For the five to seven percent of women and men who have latex allergies (redness or swelling that develops in the area that touches the latex--or close to it), there are at least two types of condoms on the U.S. market that are manufactured with an ultra-thin plastic material. Some may prefer the feel of this material to latex, and unlike latex it isn't damaged by contact with oil-based items such as skin lotions. More plastic devices are being tested and will probably be available soon.

To use spermicide or not to use spermicide

This has long been The Question. Paul Feldblum, PhD, an epidemiologist at Family Health International, says that a rigorous study by the agency showed no difference between spermicidal condoms and non-spermicidal condoms in preventing sexually transmitted infections. No such study has been conducted to evaluate the contraceptive effectiveness of spermicidally lubricated condoms. "A spermicidal condom might lend a certain peace of mind," Feldblum says, "but there's really no evidence that they are superior to non-spermicidal." In fact, some might find the spermicide itself to be irritating.

Tips of the trade

Many new condoms are differently sized and shaped with spiral tips and baggier ends that may allow a bit more friction on the tip of the penis--an element that some people find more pleasurable. However, rigorous studies that compare sensitivities in baggy and non-baggy latex condoms have not been conducted.

Female condom

The Female Condom (TM) offers women the opportunity to protect themselves against STIs and to initiate the birth control moment. Still something of a niche product, it is quite effective, almost equal to male condoms, says Feldblum. "The female condom can offer greater sensitivity and more pleasurable coitus for some people, so I would encourage couples to experiment with it," he says. "It has a plastic membrane that feels different and is non-binding, giving that friction aspect [much like baggy-tipped condoms]." Additionally, the female condom is very durable, and compatible with both oil-based lubricants and water-based lubricants.

Did someone hear a mouse?

One downside to the female condom is that it many find it, well, aesthetically lacking, so if you're having sex in broad daylight, the visual isn't quite there. "There are also issues with noise and squeakiness," says Feldblum. But the noise can be counteracted with the addition of more lubricant. Also, the longer it's worn and the warmer it gets, the better it conforms to the vaginal shape, thus diminishing squeaks.

"Slippery when wet" or "Know thy lubricant"

Some folks complain that using condoms increases vaginal dryness, making intercourse uncomfortable. Although most condoms are lubricated, a trick to making condoms more user-friendly is to add additional lubricant. Just make sure you know what kind of slippery stuff you've got, because only water-based lubricants can be used with latex. These include products like Astroglide and K-Y Liquid. The oil in products like Vaseline can quickly destroy latex but can be used with plastic devices such as female condoms.

Be correct. Be consistent.

Correct and consistent condom use reduces the risk of HIV infection by 90% or more. That's reason enough to get into the habit. Here are some more facts from Planned Parenthood:

-- The use of latex condoms during vaginal sex is effective in preventing HIV infection and several other sexually transmitted diseases, but is not as effective as hormonal contraceptives or IUDs in preventing pregnancy.

-- For some STIs, like genital herpes or genital HPV (human papillomavirus), it's not known how much protection condoms really provide.

-- All condoms are tested for defects. But, like rubber bands, latex condoms deteriorate with age. If properly stored, they should stay good until the expiration date printed on the wrapper of each condom. Plastic condoms are less likely to degrade even in poor conditions that would harm latex.

-- Condoms may be transparent or opaque, tinted, nipple-ended, rippled, studded, contoured, dry, powdered, or lubricated. Read labels on "novelty" condoms to be sure they protect against pregnancy and sexually transmitted infections.

Some condoms are lubricated with spermicide, and some people are sensitive to different brands. Switching brands usually clears up the problem.