Tongue Pull: A loop of fabric at the top of the tongue helps in putting on and removing the boots. Pull it forward and to the side and your foot should slide right in. Backstay: The back of this boot is reinforced for strength and stiffness. It gives you the support you need for any ability level. High-Density Rubber Outsole: rubber liner of this boot is extremely durable and dense for digging into the snow without slipping. PVC/EVA shell/tongue materials: Scientific blend (PVC and EVA are both abbreviations of longer chemical names) offers more durability and comfort than other, uh, less scientific materials. PVC Upper: The upper of this boot is a flexible PVC plastic, that feels about like a stiff leather. This material is highly waterproof and resists abuse well.