Evening Fedi, just wanted to show you the inside of the sweater I'm wearing right now.
It's very light, and very thin, but it's got all these little silver dots inside. They reflect my infrared back at me. They don't feel scratchy or anything, they're not like metallic, it feels like a new T-shirt, but this thing is wacky-warm. Like, it's feral rabid warm in this, this impossibly thin insubstantial thing is cosier than some of my fluffiest sweaters. It's like mithril, but for heat.
Anyway I very recommend these little spaceage silver dots. The trade name is "omni-heat" and they're pricey (this was a hand-me-down) but I bet there's knockoffs for way less that probably work just as well