Love this long sleeve crew t-shirt.  It is the perfect weight to use as a layer under many different circumstances.  We usually keep our house about 65 degrees in the winter and I wear this all the time under a flannel shirt for the perfect state of warmness.  It is great because while it keeps you warm when you are sitting still (like I am now while typing this review) you don't overheat when you start moving around.  Works great as a base layer.  I order this in the size large because I like a looser fit (The shirt is designed to be body hugging as it is insulated underear after all).  For size reference I am 5'5" and 125 lbs. with broad shoulders.  I usually wear a medium in most shirts.  Hope this helps if you are trying to figure out what size to order.  I now have several of these and after about 3 months of almost daily wear, I can say they are holding up well to washing and drying.  I have experienced no shrinking or pilling.  Highly recommended.