The interior of the sink cabinet is lined with our sink mat. The mat is a gray polystyrene mat and is used to prevent water damage. This mat is dimpled and can collect liquids up to one gallon per six square feet of mat.

Where can I buy this mat?

http://www.mockett.com/kitchen-bath-closet/pull-out-storage-solutions/undersink.html This is a reasonably priced solution.

You can purchase this through Schuler cabinetry which is available exclusively at Lowe's or you can check with other companies that specialize in kitchen solutions such as Mockett (recommended above), Hafele, Rev-A-Shelf etc.