The bestest ones I have ever bought are from the college my DD attends. They are for the drafting students, proffesional grade and double sided! One side is marked, the other is not. They measure 23 x 35" and run $22 or so!
All the ladies in my quilt group have had me pick them up-awesome price! About twice as thick as the others. The brand is Alvin.
http://www.artsuppliesonline.com/cat...?cata_id=10562
this is what they are, but those prices are about double what I pay at the college. If you have a college nearby, you could always check there!
Happy cutting!