Clyven

Design, fill, and verify down-insulated gear with engineering precision — all offline, no account required.

Clyven is the workbench companion for hand-builders of sleeping bags, quilts, puffer jackets, vests, duvets, and down booties. Enter your piece dimensions, chamber count, construction type, shell fabric, and fill grade, and the built-in LoftEngine instantly calculates the exact grams of down to load into every baffle chamber. Back-solve from a target comfort temperature to find the loft you need before you cut a single seam. Every calculation runs on-device — no internet, no subscription, no data sent anywhere.

The fill catalogue covers 12 real-world materials from Hungarian goose 850 to recycled down 600 and two synthetics, each with IDFB and EN 12934 fill-power figures. Eight baffle constructions — sewn-through to V-baffle — account for cold-bridge risk and overfill factors. Six shell fabrics track air permeability and DWR treatment so the fault-detection pass can warn you before a seam is sewn: nine checks from chamber under-fill to down leakage through a high-permeability shell, each flagged as Minor, Watch, or Serious.

Once the piece is finished and lofted, the Loft Meter takes over. Photograph the piece beside a reference card, drag three guide lines onto the image, and Clyven reads the loft in millimetres and back-solves the fill power your piece actually reached versus the label claim. Track loft over months to see how a sleeping bag ages, archive completed builds, and dial in the next one. Unit toggles for °C/°F, mm/in, and IDFB/EN 12934 re-render every readout instantly. Built-in care guide and kit list keep your down performing season after season. Clyven is the precision tool the cottage-industry sewing community has been waiting for.