In order to be certain your package will arrive on time and your customer won't be charged additional shipping, it is important to use the correct packaging materials. First Class package service requires your own packaging, and you cannot use or reuse a Priority Mail box or mailer to send items first class. All of the USPS Priority Mail options in PopItUp have their own designated packaging which you can obtain for free from USPS. You can pick up many materials at your local post office, or you can order them from to be delivered to your home at no charge. Click the names below to open a link to the USPS site to view details and order supplies.