BQuality Park Tyvek Open End First-Class 10 x 13 Inch White Envelopes 100 Count (R1590) ReviewbP PP Quality Park Tyvek Open End First-Class 10 x 13 Inch White Envelopes 100 Count (R1590) PTyvek� white envelope with a 14-lb. paper stock.PTyvek� exterior.PLightweight.PDurable and reliable.