A method of manufacturing a modular box assembly comprises constructing an insulation batt by combining thermoplastic binder fibers and reinforcement fibers in a fibrous web and heating the batt to a temperature exceeding a glass transition temperature of the thermoplastic binder fibers and melting of the thermoplastic binder fibers. Pre-laminated material is constructed by attaching a first sheet in facing contact with the insulation batt and attaching a second sheet in facing contact with the insulation batt opposite the first sheet. The pre-laminated material is cut to size to define first and second laminated members. Portions of the laminated member are folded to form first and second thermal liners. The first and second thermal liners are positioned in a box cavity defined by a box such that the first thermal liner and the second thermal liner together form an insulated cavity within the box cavity.