100 – 9″ x 11.5″ Stayflats Plus Kraft Mailers. The 2 PSK is the same size as one of our original Stayflat Mailers. To this day, it is the standard size in the industry to send 8-1/2″ by 11″ photos. Made from durable .028″ Tan Chip paperboard, the protection of your important photos is assured. It’s also environmentally friendly and 100% Recyclable.