The Stylist Pen package declares that it is water resistant. I don't think there's much evidence of that in this sketch of the Northern Shoveler I photographed a couple of days ago. The pen is a very inexpensive felt tip which I purchased at the University Book Store. I drew first with the pen, which creates a lovely elegant thin black line, and then added water to it to dissolve some of the lines. I especially enjoy the blue green color that is the result of dissolving the black line.
I love the Stylist for quick outdoor sketches-- you can add water to it on the spot or later when you get back to your camp, hotel room or studio. It's a very lightweight way to go!