All our cards are printed on Crane's Lettra, which is a wonderful 100% cotton paper made by Crane specifically for letterpress printing. In Crane's words, "Crane's Lettra® is the only paper developed expressly for letterpress printing with a special texture that maximizes the letterpress imprint."
At Hoban Press, we've tried a variety of cotton paper and have found Lettra to be the most versitile and beautiful for calling cards and small stationery items.
220# Paper Upgrade
When ordering calling cards, there is an option to upgrade the paper to 220# (600gsm) Lettra. This option will give you a stock that's twice as thick as the standard 110# (300gsm) that comes standard. We often liken the thickness to a paper beer coaster you'd find at a pub. They certainly get noticed and add a bit of durability. If you need to carry many cards with you at once, it may be better to stick with the standard 110# stock.