Condom facts

I think most people know the basics of condoms: made of latex, roll them on, they offer protection against STDs and pregnancy, but there's a lot more to them, that people don't always know.

Reservoir tips
The vast majority of condoms have a little nub at the top. This nub is called the reservoir tips and is used to collect semen. When a condom is put on, the reservoir tip should be pinched shut to leave room for the semen (instead of filling it with air which makes it more likely to burst).

Spermicide
Commonly added to condoms, spermicide is flavorless and kills sperm to prevent pregnancy. Unfortunately spermicide can cause vaginal (or oral or anal) irritation, causing infection and making it easier for STDs to be caught, particularly HIV. Spermicide condoms should not be used for anything other than vaginal sex. Some schools of thought argue that spermicide should never be used at all.

Doubling up
If one condom gives protection, won't two give twice as much? No. Layering condoms increases the chance of them tearing.

Lubricants
Oil-based lubricants can damage latex condoms. Be sure to use water- or silicone-based lube. Oil-based lubes include hand oils and vaseline, so think twice before using a home-made lube. (Silicone lubes can also damage sex toys, so check for that.)

Latex
The standard material for condoms, it is cheap, flexible and relatively thin. Condoms from latex protect against STDs and pregnancy. The downsides to latex are the smell and taste (particularly for oral sex) and allergies to it are common. It also does not conduct heat well.

Lambskin
Actually made from sheep intestines, lambskin is an option for people who are allergic to latex. Lambskin condoms are thicker than latex, and more expensive. They protect against pregnancy but don't provide as much STD protection as latex. Historically, this is what people used

Polyurethane
The standard alternative to latex. Polyurethane condoms conduct heat better than latex ones, can be used with oil-based lubes, and lack the gross latex smell. Unfortunately they are more likely to break or slip off during sex. They are also more expensive

Polyisoprene
The newest condom material. Made of synthetic rubber, polyisoprene condoms have all the advantages of polyurethane without the increased risk of breaking. They are also much thinner than both latex and polyurethane condoms, without adding any risk. The downside is they cost more, and none of the bells and whistles of latex condoms (flavors, extra shapes, ribbing, sizing options, etc.) are available.

Remember that "perfect use" and actual condom use have very different failure rates. By paying attention to how you use condoms, you can greatly improve the protection you get.

Image source: http://www.tac.org.za/community/taxonomy/term/63