There are several kinds of paper you can use for your invitations, the standard blank paper stock and a complete range of designer papers. The 3 most popular paper stocks are 65# cover stock, 90# index card stock, and 60# - 70# vellum bristol stock. Most companies that specialize in custom invitations and stationery will have a wide selection of paper types to choose from. They'll be able to help you find the right type of invitation for your occasion.