Quippywrote a review of Airblaster Merino Wool Ninja Suit - Men's on November 4, 2014
One of my most tried and true, must-have pieces of winter gear ever! And fall and spring too I might add. THe design of the Ninja Suit is really dialed. The hood is key, easy on, easy off, stretchy and fits perfectly, great for on-th-fly temp regulation. One piece design is awesome, seals out cold air or snow 100x better than separates (top + bottom), 4-way stretch material is unrestrictive and comfy. How to go to the bathroom, #2 for guys and both for ladies? Its so easy. I'm pretty sure its faster than separates, no untucking, re-tucking. Just unzip the waist / hip zip and sit or squat!! Anyway, a Ninja Suit is a MUST HAVE, and the MERINO version is 110% awesome!!
I'm 5'7" 175 and wear a medium. It fits well. I'd say they run 1/2 size large, at least if you want it snug. But I recommend having a little room in it, as you'll want to wear your Ninja Suit solo to your apres activity of choice.
Layering: Normal winter day, I wear mine with a thin merino T and boxer briefs underneath. That is enough heat for me 99% of the time, but its generally no colder than 20F where I live. Also, with the under layers, I don't have to wash the Ninja Suit that way for a loooong time.