I have had trouble with poor circulation in my hands (Reynauds Syndrome).  My research has indicated that maintaining core temperature should help keep the blood flowing to the extremities.  I work in a very large, inadequately heated building and frequently have to hold my hands under warm water for several minutes to stimulate the blood vessels into reopening.  I normally can't work for more than an hour or so below 50 degrees without losing feeling in 2 or 3 fingertips.  Yesterday, it was 32 degrees when I got up, so I put this shirt to the test.  I could feel the difference as soon as I put it on.  I worked all day and drove home without a single fingertip turning white.  I will be ordering some more.