A compromise — #16 of 31 Chiffon ranks #16 of 31 fabrics for warmth without weight. It is a middling fabric for this. Ranked on warmth relative to weight, with a packability bonus. The top pick is Cashmere.
Chiffon measures 78/100 for breathability, 8% moisture regain, 20/100 warmth, at 50 gsm. Warmth-to-weight is the metric: 20/100 warmth at 50 gsm is an excellent ratio for packable insulation.