Like a classic cotton cap, arm warmers are a riding essential. Designed primarily to regulate your on the bike temperature, they might quickly become your most used piece of cycling apparel.
Most cyclists keep a pair of arm warmers in the rear of their jersey at all time. Climbing a mountain will make you hot, but that sweat will quickly cool on the descent and start to bring your temperature down. Keeping a pair of arm warmers to hand will ensure that you can descend at speed without losing temperature. Of course with variable weather patterns, many riders leave and return home still wearing their arm warmers, with a good pair allowing excellent moisture transportation and all day comfort.
The biggest difference we see in arm warmer construction is stretchiness, and this stretchiness translates to an arm warmer that is unlikely to slip down mid ride, and thus maintain its position on the upper arm all day. Other riders though prefer some weather protection in their arm warmers, so just look at a product's detail page for more info if that is what you are looking for. Which ever arm warmers you choose though, just remember that from mountain descents to cool starts, they are an adaptable and essential piece of clothing for all road cyclists.