A thin nylon windshirt and a base layer shirt can keep you comfortable in surprisingly chilly weather, as long as you are on the move. Kebnekaise area, Swedish Lapland.
Like on all my garments I find that a hood adds warmth enough to more than offset the extra weight. This one is a Marmot Trail Wind Hoody at 155 grams (5,5 oz).
Comments and current insights: I find the windshirt a most versatile and excellent garment and I use it a lot. It dries out really fast if it gets damp underneath the umbrella or in the packraft.It breathes much better than my rain jacket, which makes the latter one a bit sweaty to hike in. In warmer climates you might do very well without a windshirt, but in artic regions I tend to wear it almost all the time together with my base-layer undershirt.