Iridium. A dense, very hard, brittle, silvery-white transition metal of the platinum family, iridium is used in high-strength alloys that can withstand high temperatures and occurs in natural alloys with platinum or osmium. Iridium is notable for being the most corrosion-resistant metal known.

Some cars are difficult to replace or clean the spark plugs and a longer performing plug is worth the price. Once a vehicle is old enough to start leaving deposits on the plugs, cleaning would be a better solution. The guanantee is probably minimal to protect the manufacturer from heat cracking the ceramic.

http://www.densoiridium.com/images/iridium.gif

Iridium is just an element that can withstand higher temperatures and is corrosion resistant. It isn't going to make a car burn hotter or be any better for combustion. Just having good plugs provides better combustion, regardless of type. If a plug is fouled by deposits, it doesn't make a difference what it is made of, or what it costs. Most people just replace plugs and don't clean them. All a plug is doing is creating a spark to ignite the fuel. If the gap is maintained on the crapiest plug made, on the oldest engine, it will still work the same as a good, expensive plug. Cheaper plugs stand a better chance of being damaged by high temperatures and need the corrosion filed off, over time. Most people just clean and replace them when needed.

Get them someplace else. Be warned. Some manufactures will not honor any engine warranty issues with them. Why? Because they can. I run them in several cars with no issues and they don't cost anywhere near that. The Iridium is supposed to be the best current conductor on the market. Gimmick? I haven't noticed any real difference in power or mileage, but decided to try them anyway.

they recommend nippondenso, I like autolite. the autolites are 8 bucks and the nippondenso's are 27 what could the difference be? Oh brainieack one

also pb are carbon fiber/metalic brake pads the same as ceramic?

Supposedly you get better spark for better combustion thereby giving you better mileage and performance. But for that cost it would take a long time to recoup any savings. You don't say what type of car you have. Plugs last nearly 100k nowadays so it would be hard to justify the extra cost for something that only lasts 30k. If you want a quick fix for mileage and performance, install a K & N high performance air filter. I have always gained about 2-5 mpg.

Burns(spark) hotter....better for combustion