Expandable Corrugated Mailer-25/bundle (12 1/4 in. X 14 1/2") Rigid Construction - Made from durable 29ECT e-flute corrugate Max 2 Expansion Capacity - to hold a little or a lot! Patented Design - 360 Perimeter Protection (no shifting, no corner damage) Hotmelt Closure - Secure closure that will not open during shipment. E.Z. Open Tearstrip - Convenient opening without the use of sharp utensils.