All containers are of one piece, seamless molded construction with thick insulating walls of expanded polystyrene (0.19 "K" factor). Supplied standard with outer foam plastic surfaces protected with durable 275 lb. test laminated fiberboard case. Lids are tight-fitting and of the same insulation thickness as the other insulating walls. Insulation is non-settling, non-deteriorating and maintains its K factor and efficiency throughout the life of the container. Easy rolling dollies (optional) makes larger models completely mobile.