I've been using these arm warmers for cycling in South Lake Tahoe's bi-polar Winter/Spring for the last month. From 2,100+ miles of backpacking I've learned that less is more when it comes to clothing for high-output activity. When it's hovering around freezing or just above, I prefer layers of merino rather than a windshirt or jacket. If it's sunny and 40+ I wear my Icebreaker Circuit jersey and these arm warmers. For anything colder, I wear a 200 weight Contour Crew as a base layer in addition to my jersey and these sleeves.
Basically what I'm getting at is that these arm warmers are super comfortable and warm - but more importantly, they are breathable. They are great to have around for changing seasons and as a permanent piece of cold-weather kit.
I'd also recommend these for backpacking to replace a long-sleeve shirt.
Peace and love