12x15 1/2 clasp envelopes have durable 2 prong metal clasps and reinforced eyelets for repeated access (Quality Park); 10x13 clasp envelopes have double prong metal clasps and reinforced eyelets, reusable (Quality Park)
32 lb heavyweight kraft paper is opaque to protect contents (12x15 1/2); 32 lb heavy-duty brown kraft stock stands extensive handling (10x13)