400 – 9″ X 6″ Stayflats Plus White Mailers. Our 19 PSW features the opening on the long side for easier fulfillment. The 9″ x 6″ size will hold an 8-1/2″ x 11″ letter folded in half. It’s the perfect way to send out CDs or other items with an accompanying cover letter. Made from durable .024″ CCNB paperboard, it’s an environmentally friendly and 100% Recyclable.