Go back up to the first threads for sizing recommendations. Here's some more info. I wear a women's medium and have the medium armwarmers.

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Arm warmer sizing
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Lying flat on the table, the width of the top/bicep end and then the lentgth:

XS - 4 1/8" wide and 17" long
S - 4 1/2" and 17 1/4"
M - 5" and 18 1/8"
L - 5 3/8" and 18 3/8"
XL - 6 and 18 3/8"

The fabric is a nice thick lycra with a fuzzy interior. Should be really nice for the coming colder weather (or current cooler weather for those down under).