The Grubs Frostline wellingtons use their self-insulating insu-foam ultra bootie construction which acts as a neutral medium between the wearer and the outside.

The bootie is both waterproof and insulating and exceeds the long-term effectiveness of waterproof membranes and lofted insulations. The boots are waterproof to EN ISO 20344: 2004 5.7 standard. Featuring a super stretch Chloroprene material, covered with a 4 way stretch knitted nylon jersey which can expand not only in width but also height. INSU-FOAM ULTRA™has a fine micro cellular structure, which stops heat transfer through its structure.

The microscopic bubbles of air are so small that it is waterproof even in 3.5mm thickness.