I'm 6'4" 220 I am thinking an xl. Any idea on how much this weighs in the xl size...wanna use it for backpacking.

According to the size chart (click "view size chart" above the big green Add To Cart button) you're on the top end of the XL size. You should be just fine there. A couple "howevers" though... 1. we only have XXL in stock right now since this item is last season's model. The new ones should be arriving any day now. 2. The Merino Ninja Suit is far superior! I have owned both. The merino material regulates body temp naturally, wicks moisture better than synthetic, and is MUCH warmer. The merino material is buttery smooth and not itchy at all. Also, we have all the sizes in stock of the Merino version. I strongly suggest the merino - you will be so glad you did. Check it out here... http://www.dogfunk.com/airblaster-merino-wool-ninja-suit-mens oh yeah- the suit weighs between 1.1 lbs for size small 1.8 lbs for XXL.