Climbed Kilimanjaro and used this as the layer over my long underwear top and down jacket.  Was never cold.  And the micro dot technology on the pants worked out great, too.  That, no doubt allowed me to use one less layer.  For the guy who gave it a bad review because he used it as a shirt for running a marathon--it's a great product but you used it for the wrong application.  That's like saying a Ferrari is a bad car because you tore up the under carriage taking it off road.