A solid choice — #15 of 31 Silk ranks #15 of 31 fabrics for warmth without weight. It is a good fabric for this. Ranked on warmth relative to weight, with a packability bonus. The top pick is Cashmere.
Silk measures 60/100 for breathability, 11% moisture regain, 30/100 warmth, at 90 gsm. Warmth-to-weight is the metric: 30/100 warmth at 90 gsm is an excellent ratio for packable insulation.