It runs a size small and still a snug fit but wouldn't want it loose so it heats better being close to your body. I waited to review it because I had bought 2 of another brand and both quit within a month. I even got an exchange for one and it quit too. I also bought the jacket in this brand and it is awesome too. My wife also has the vest and jacket. We are very pleased with its performance. We bought extra batteries because we wear them a lot so we needed ones that could hold up to our lifestyle. They are made very well and are light weight. They are warm without the heat as well. When it was down in the teens and lower 20's we put a fleece jacket over the vest and was even more toasty warm trapping the heat. We are very satisfied and have had no issues with these so far. We also love the mobile phone app to control our vests and jackets. Price was great allowing us to buy multiples for different uses. We are happy we found these that do what they say and last us with the amount of time we use them.
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