Protect your knees from the cold on descents and chilly morning rides a set of knee warmers adds versatility to your bib short and are great for spring and autumn climates castelli39s nano flex knee warmers are highly water resistant and thermal giving you premium protectionmore flex more nanonano flex knee warmers have been in castelli39s collection for seven years and they have now found a way to improve them introducing nano flex knee warmers with an added insert on the back in