Embodiments of the present invention replace relatively bulky nonwoven thermal insulating materials used in thermal liners with thin, lightweight, flexible films that maintain or improve TPP performance while reducing the thickness, and enhancing the flexibility, of the thermal liner so as to increase wearer comfort. Moreover, the films incorporated into the thermal liners can be both air and vapor permeable such that the TPP performance is not realized at the expense of THL performance. Rather, the THL performance of garments incorporating embodiments of thermal liners contemplated herein is comparable to - if not improved over - garments formed with traditional thermal liners.