From their website:
We're proud to be the first print shop in the U.S. to offer printing on a luxury bamboo paper.
What is our bamboo paper like? It's extremely soft, luxuriously thick, and elegantly textured. It's also perfect for letterpress. Essentially, imagine the highest quality cotton paper. Now imagine something even prettier and without the pesticides used in cotton production.
They also have a social stationery collection which is equally as fantastic. If you are in the market for new stationery, Smock is definitely worth a look!