Best in Test BootExtreme 2.0 is a warm thermo boot full of smart details. Extreme is approved by the German organization TÜV SÜD, which inspects products and issues product certifications in safety and sustainability. Thanks to a Polyurethane construction with an adjustable cuff lock, Extreme 2.0 is waterproof, light, and comfortable for all-day wear. Made from a flexible Polyurethane called Elastopan®, which is a 100% PVC-free, it contains millions of tiny air bubbles and is 4% lighter than PVC or rubber. Viking thermo boots provide 2.5 times more insulation than normal PU boots and are twice as durable. With the help of a wool and polyester lining, Extreme 2.0 can effectively insulate kids feet down to -20°C. The sole of this boot is made from TPU, which is slightly heavier than PU, but has excellent wear and non-slip properties. For blocking wet, snowy, and frigid conditions, Extreme 2.0 is a tried and trusted winter classic.Wool Blend LiningHigh Isolation Material (BASF)Snow Lock