A modular box assembly includes a box with side panels defining a box cavity, a first thermal liner positioned within the box cavity, the first thermal liner including a first insulation batt disposed between sheets, the first thermal liner defining three first liner panels, at least one box side panel being covered by a first liner panel, and a second thermal liner positioned within the box cavity, the second thermal liner including a second insulation batt disposed between sheets, the second thermal liner defining three second liner panels. At least one other of the side box panels is covered by a second liner panel. The bottom box panel is covered by either a first liner panel not covering any side box panel or a second liner panel not covering any side box panel. Each insulation batt can be formed from a mixture of thermoplastic binder fibers and reinforcement fibers.