• 4-5 hours of near zero temperatures and constant rain? I run pretty hot, but I haven't found any arm warmers that would work for me in that.

    IME Nanoflex are good, but they are just normal Roubaix warmers, with a bit of silicone on the fabric so that most of the water runs off. Good for warmish wet days, and for quick blasts, but not enough on their own for long winter rides. That's not what they're made for though.

  • 4-5 hours of near zero temperatures and constant rain?

    I wouldn't expect arm warmers to handle that alone. My choice would be one of:

    • Classic jersey, arm warmers, wind or rain jacket. Rain jacket being warmer.
    • Long sleeve merino jersey, wind or rain jacket.
    • Long sleeve merino base layer, softshell.
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