Tonight I conditioned the leather in my car in preparation for winter. In general, I only condition the leather in my M coupe once per year. My Volkswagen is my daily driver, it goes to Home Depot and who knows where else, and it gets conditioned twice per year. The most common mistake people make when taking care of leather is using too much conditioner. Leather (non-suede anyway) comes with surfactants (protection) from the tannery. BMW leathers are all very well protected when new. If you apply too much leather chemicals and/or too often, you will strip off the protection the tannery applied. Your leather will crack and wear prematurely. The best analogy for this is like enamel on your teeth. Once the enamel is gone, your teeth have no defense. At any rate, I do care for my leather many times during the year... I just don't apply chemicals. The best thing you can do for leather, to keep it soft, matte-finished, and supple, is to wipe it down with a damp cloth whenever you think to (i.e.: every wash). Wiping leather with a damp cloth will pick up any loose dirt particles. Loose dirt, between you sitting in the seat, and the leather, will buff or polish the leather. It will get shiny and become thinner because of this polishing action. I use an all-cotton diaper when I wipe down my leather and I do it softly.

Anyway, the following techniques are what I use when working with chemical treatment. As always, feel free to do it your way. This is the LeatherZ way.

I use Spinneybeck Leather Cleaner, Conditioner and Protector. Spinneybeck used to sell a dedicated cleaner and a dedicated conditioner, but they reformulated their product after some people went overboard on the cleaner. Obviously I have not used every leather chemical on the market, so I can't speak to what is best. In addition to Spinneybeck, we also like Connoly Hide Food and recently I was impressed with the Griot's leather treatment product. I always use a 100% cotton diaper to apply and to buff when using leather chemical:



You should apply leather chemicals when the seats are warm. If you park with the windows rolled up, the seats will get warm. If you have a heated garage, the seats may be warm. In a pinch, you can use heated seats to warm the leather. The leather doesn't have to be hot, but the idea is when it's warm the pores will open and the leather will absorb the chemicals better. Too cold and the chemical will just sit on the surface.

Before you start, vacuum all loose particles. Wipe leather down. Inspect for dirt. If the water can remove it, use it. If not, wait for the leather chemical rather than polish feverishly.

This is my driver's inboard bolster before any chemicals:



I always work in one panel at a time. I try to avoid getting leather chemicals on the stitching or in the seams. It can discolor some threads. If chemical gets in between panels, it maybe difficult or impossible to get out and it could even weaken the backing at the seam. This amount of Spinneybeck is enough to do this panel:



Apply it in small circles. Press softly, but press enough to work the chemical into the leather. When fully applied, the panel will look a little wet but not soaked (note flash is on in this pic):



I generally apply chemical to one half of the car at a time. Since mine has a lot of leather, this takes about 15 minutes. By the time I am done, it's time to start removing/buffing off any excess. I use a new diaper for this. Again, small circles, inspecting closely for any globs of chemical. End result:



You should not have to buff much, if any -- provided you did not apply too much chemical to begin with. It's exactly like waxing the exterior. One thin coat of wax on your paint is just as effective as one massively thick coat. It all has to be buffed off in the end, and the more you have to buff the more likely you are to screw something up.

After the whole seat is done:



I try to not sit in my car for at least 24 hours after applying conditioner. I want it to soak in as much as possible.

Pay special attention to high-wear areas like steering wheels or knee bolsters like M and Extended Leather cars have:



Even in my car which is usually at a "surgical" level of cleanliness, conditioning will pic up dirt particles:



Hope this provides value to someone.