The G1561 thermal liner made of 400 g recycled Primaloft insulation. Unlike natural materials such as felt or wool, it will not retain any moisture near the foot. These materials attract and retain water, while our insulation will expel water or moisture to the outside while retaining your warmth. By staying dry, the thermal performance of the boot remains optimal. In addition, its reinforced heel allows for better durability. Firm, but elastic, it will mold to the shape of your foot, ensuring maximum comfort and warmth!