These cases hold 16 x 20 inch mounted prints and are 4 inches deep. The outer shell is rigid polypropylene and the inner liner (replaceable) is cardboard. Nylon quick-release straps close it securely and there is a slot for an address label and a carrying handle. Corners are steel-reinforced. These are well-used and look it, with scuff marks, tape remnants, and old postage stamps, but they are structurally sound. New these cost $350 each at B&H (Fiberbilt by Case Design P50 Versatile Mount and Print (bhphotovideo.com).
$95 each or the pair for $175, plus shipping (US only)