Warm breathable arm warmers with castelli39s advanced nano silicone treatment for fantastic water resistance nano flex fabric behaves just like thermoflex fabric in dry conditions but provides unbelievable water repellency when it starts to rain more flex more nanonano flex arm warmers have been in castelli39s collection for seven years and they have now found a way to improve them introducing nano flex arm warmers with an added insert on the back in nano light fabric to help them b