Rab Strata Flex Jacket Men's. The Strata Flex Jacket is a versatile mid layer jacket, using innovative Polartec Alpha synthetic insulation, designed for climbing and fast moving activities. The Strata Flex Jacket also features Polartec Power Stretch side panels which offer extremely high levels of freedom of movement, lending the jacket to technical climbing and fast and light ascents. A wind and water resistant Pertex Microlight outer fabric offers light weight protection, while technical details include thumb loops, YKK zips throughout and a slim fit for comfortable layering use. Extensively tested by Rab athletes in conditions as harsh as Arctic Norway, the Strata range revolutionizes how synthetic insulation is used in the mountains.