Planning my first down build. I bikepack in Portugal (warm coastal summers ~15–20°C, mountain winters ~0–5°C), am 170 cm tall, and sleep warm. Low packed volume is top priority.
I’m designing a 3-piece modular system using 800+ FP down and box baffles (no sewn-through seams):
Main Underquilt (~5°C / 40°F): Simple rectangle (165 × 105 cm) with a width-wise differential cut (outer 115 cm) and ~8 longitudinal baffles.
Modular Blanket (~5°C / 40°F): Snaps onto the main UQ (Gemini-style) for sub-zero winter trips, or works solo as a warm-weather quilt.
Winter Top Quilt (~0°C / 30°F): 185 × 135 cm, non-sewn footbox (KAM snaps + drawcord) to open flat, plus pad attachment tabs for ground sleeping.
Seeking your input on:
Temp ratings & loft: Do two ~5°C layers reliably hit ~ -5°C (20°F) when stacked? What baffle heights and fill weights (800+ FP) would you recommend for 5°C vs 0°C?
Suspension: Traditional full-length side channels vs. Clew suspension—which is better for a modular snap-on setup and bikepacking packability?
Snapping layers: Any tips on KAM snap spacing/tabs to prevent the outer blanket from compressing the inner UQ's loft?
End draft collars: Essential on a rectangular 5°C UQ, or do shock cord end cinches suffice?
Features: any nice features on your underquilt that you like (clips for the hammock or alike)
Pics & Schematics: If you've built a modular UQ, clew setup, or differential-cut rectangle, please share photos or sketches!
Thanks for any insights!