A school bus seats, comprising: a seat back, support legs
, a seat bottom and a one-piece integral envelope cushion completely residing over said seat back, said envelope cushion includes an integrally molded polyurethane foam having anelastomeric skin formed on the exterior thereof; said seat back is a sandwich composite, and includes an aisle-side bracket interconnecting one of said support legs and a window-side bracket interconnecting the other of said support legs by pinsselected from the group consisting of hollow pentagonal, hexagonal, heptagonal and octagonal pins; wherein said sandwich composite seat back is ultrasonically welded to said brackets.