The following information was provided by Manduka. These tips are for the Black Mat Pro, the Manduka Pro Mats, and the ProLite Mats which are all made of the same material but are different widths and thicknesses.
There is a break-in period that everyone, including those who are on our mats, has to go through before the thin film wears off and the slipping is almost completely eliminated. Typically, it takes about three months of daily practice and a "little" bit of slipping during that time so that the friction of feet and hands wears on the mat.
Once the mat is broken in, if you sweat a lot, there still might be a slight amount of slip in some standing poses and poses like down dog, but if you keep your awareness and energy moving towards, instead of away, from your center of gravity, the "slippage" stops and one can stay firm in the pose. Actually, a little slippage comes in handy on some poses, for instance shoulder stand or plow pose, when it's nice to allow the head to slide and the neck to lengthen.
Use it! Our customers have found that the best way to “break in” their mat is to use it on a daily basis.
Another trick is to leave it in the sunshine for an afternoon or sprinkle sea salt on the top surface of the mat, dampen with a cloth, and scrub it with a stiff scrub brush. (If following this trick, repeat this tactic 3 times, not just once, and you should see improvement.)