A mat occurs when hair twists together into tangles and knots. These knots twist together and form mats. They usually feel like clumps when you pat your pet. Sometimes the mats lie close to the skin and while the outer hair feels brushed out, underneath it is like a twisted carpet of hair. If you cannot run a fine-tooth comb through your pet’s coat, to the skin, chances are there is matting, or excessive undercoat, or a combination of the two.