There are a few types of leather used in automobiles. The main two seem to be;
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Full grain (naked) leather: The top o' the line in leather! BMW's Nappa leather is full grain. Open pores in the leather to allow to "breathe". This leather should display the natural markings and grain characteristics of the animal from which it was taken. The best leathers are clear, clean, and supple. The better the quality of hide or skin, the less it has to be treated. The natural grain variations should be exposed. One should see the "fat wrinkles" and the feel should be supple and natural to the touch.
-Corrected Grain (finished) leather: BMW uses this for the Steering Wheels, Shift Boots, Emergency Brake Boots, and Shift Knobs. Even though all hides feature the natural markings of the animal, some of these less desirable marks are buffed out to create corrected grain leather. Corrected grain leather offers the sturdiest finish and is the most economical leather. This leather will have a very uniform surface but will deteriorate under flexing due to the dense finish coat.
Leather Care; Leather is an extremely durable material. However, leather does need to be cared for. Body oils, dirt and perspiration in high wear areas can clog the natural ability of leather to breathe. This grime can migrate through the top coat and cause the lower layers to separate. A regimen of cleaning will remove the body oils and dirt, this will in turn prevent damage. Abrasive detergents, saddle soap, solvents and silicones should be avoided.
A quick wipe down with a soft 100% cotton face or hand towel that has been wet down and FULLY wrung out should be performed at regular intervals to remove surface dirt before it has a chance to become imbedded. Two to three times a year, you should use a dedicated leather cleaner followed by a moisturizer.
Leather Care Products;
Lexol: (one of the most known names); These products are preferred for corrected grain leather, but can clog the pores of full grain leather. This will inherently cause damage to the leather layers. Supposedly, Lexol will recommend that you do not use their product on BMW's Nappa leather.
Spinneybeck: A newer name in auto leather care, but has been highly recommended by LeatherZ. I haven't personally tried Spinneybeck's products, but they do sound like quality products.
Leatherique A new name to most folks, but they have been around for over 30 years! I have tried their products and find them to be everything that they claim. Several auto enthusiasts clubs swear by Leatherique products. Their formula is based on a natural old Swedish Secret and is a complex blend of proteins and collagen that actually restore the tensile strength to the leather, not just sit on top and make it slick and greasy. It does not harm carpeting or headliners and will also soften rubber door trim and vinyl. Repeated applications, with sufficient permeation time are required for cardboard hard, neglected leather.
Links:
http://www.leathermotive.com/leathercare.html
http://www.leatherz.com/leathercare2.htm
http://www.crownltd.com/MaintLeather.htm