No Strings Attached! Not everyday calls for things to be laced up, tightened down and serious. Sometimes it's nice to be able to toss your boots on, or off easily, with comfort to spare. That's why Danner built the Mountain 600 Chelsea. Danner borrowed the ultra-cushioning Vibram SPE midsole from our award-winning Mountain 600 to provide daylong comfort. For the sole, they kept the same lightweight, but grippy, Vibram Fuga outsole that makes the Mountain 600 so capable.