In parts of Northern France and Belgium there exist roads made of cobblestones that have lasted for centuries. DeFeet made ArmSkins to stand up to the punishment that these roads and the inclement weather dish out.
The way to tell if an arm warmer is up to the job is the slip test - if it starts coming down mid ride you've got a problem. However, in this regard DeFeet are pretty confident about their abilities (showing skin between your arm warmer and jersey is simply not done), and proudly proclaim that there hasn't been a road or trail made that will upset the fit of the ArmSkins.
Soft and super stretchy, the DeFeet Merino Wool ArmSkin, whether worn from the outset or kept in a rear jersey pocket for drops in temperature, is simply a ride essential for changeable conditions.