Postcards can be printed 1 or 2-sided and are often used as a mailer. This is mainly because unaddressed admail is cheapest than traditional mail and post cards do not require envelopes. Club promoters also use post cards often to promote special events or nights at a club. They come in various sizes and coatings to enhance the effectiveness of the product. Rounded corners are also a popular option. This is also used frequently as a counter top or tradeshow promotion tool.