Some people don't like zippers, but they act as a thermostat for controlling core temps to reduce sweating. The 400 allows complete venting and easy removal, where the 200 is a pull-over and quarter zipper. Temperature range and level of activity are considerations. I started with a 400 and I am glad I did so, but it is the coldest part of winter here.
Answered on 1/21/2011 by Cary from Indiana