R1 plus R2 equals R4. That's not bad math, it's good insulation. R4, the newest in our Regulator'· fleet, is warmer than Synchilla\' fleece, breathes better, dries faster and blocks the wind. To prevent wind borne chill, we sandwiched a Polartec· Windbloc laminate between smooth, midweight R2 polyester on the surface and a lighter, moisture-wicking R1 grid on the inside. The Windbloc preserves your body's precious thermal envelope without bulking you out or restricting your freedom of movement. Wear it alone or layer it under a shell when you need full foul weather protection. Made in USA. M's R4 Jacket