I need to know the answer to this too...
My yorkies have two very different coats. My now deceased and Mariposa both have the type of coat you are talking about. I had heard that it was a cotton coat. But it does not mat (unless after wearing garmets) but then combs out easy enough.
Now Angel Baby, I 'thought' was a silky coat, but seems to have this 'under' stuff that REALLY matts! It's awful to the point that I am going to have to keep her cut short just to deal with it. So maybe she has the cotton and Mari has the silky???
I would appreciate help on this...thank you