Kirk W wrote a review of Outdoor Research Helium II Jacket - Men's on September 8, 2014
Familiarity: I've put it through the wringer
Fit: True to size
This is a great lightweight rain jacket that offers good performance for its weight. Just be aware that it might not perform in a sustained deluge.
Performance: I live in a dry western state where we aren't generally subject to heavy sustained rains. In this situation, what is required is a light jacket capable of protecting you from light rain or an occasional heavy downpour of limited duration. The Helium II fits this description almost perfectly. I've worn it in light rain, short duration cloudbursts, and surprise summer snowstorms and have stayed dry with no problems. Where I did encounter a problem was during a multi-day trek in the Alps where we had rain all day. In that application the jacket wetted out. Fortunately the two days this happened were followed by nights in a hut where I could dry the jacket out.
Fit: The size large fits my 6'2" 175 lb frame just about right with enough room to layer a t-shirt and light fleece underneath. The size large weights 6.3 oz on my scale.
Application: This jacket offers a lot of performance for its weight and is great in light rainfall, short cloudbursts, and even light snowstorms. It'll be in my pack whenever I feel I might encounter these conditions, but I'll pack something more substantial the next time I trek to an area with the potential for substantial or sustained rainfall.