# Northstar Roll-Top Wallet — Design Spec v0.2 > **This document is the card wallet, not the phone pouch.** Two different > products share this folder. This one is the locked v1 per `DECISION.md`: a > 100 × 70 mm card wallet with a dry bag welded to its bottom edge, no window > and no electronics. The window-bezel variant that `DECISION.md` parks as v1.1 > is drawing `D14-RT-003` — see `derived-dimensions-revC.md` and > `renders/D14-RT-003-revC.png`. Do not cross-read dimensions between them. > v0.2 reconciles this document with the parametric CAD model in `cad/`. > Building the model corrected four things: the closure mechanism, the panel > length, the loaded thickness and the sealed volume. See §9 for the log. A slim everyday card wallet with a waterproof roll-top dry bag permanently attached along one edge. Stowed, it reads as an ordinary minimalist wallet. Deployed, it swallows a phone, keys and the wallet itself and seals watertight. Source: hand sketch in `reference/original-sketch.png`. --- ## 1. Reading of the original sketch | Sketch element | Interpretation carried into this spec | | --- | --- | | Hatched cylinder at the edge of the front view | Dry bag rolled into a compact cylinder, stowed flush against the wallet | | Spiral in the side view | Roll cross-section, ~4–5 turns | | Annotations "4" and circled "5" | Number of roll-downs required to seal | | Long arm with curved arrow | Closure strap swinging over the roll to the buckle | | Circled "1" / "2" on the flat strap | Strap and buckle hardware callouts | | "Waterproof" | Welded-seam construction, no stitch penetrations below the waterline | ## 2. Core architecture The wallet is the **anchor plate** for the closure. The bag welds to its full bottom edge, and the strap that clamps the roll bar-tacks to the wallet itself, so no separate closure hardware is needed and the roll always compresses against a stiff flat surface. An earlier draft of this spec claimed the wallet *was* the roll core. That is not buildable: the wallet is 70 mm tall and stiffened with HDPE, so it cannot wrap into a 25 mm roll. The bag's mouth rolls up against the wallet instead. **Stowed.** The whole bag spirals into a 12.4 mm cylinder sitting flush under the wallet's bottom edge, strap over the roll, buckle clipped on the front face. Card slots stay accessible without unrolling. **Deployed.** Unclip, unroll, and the bag opens downward into a 280 mm tube. Load it, roll the mouth up against the wallet four times, and clip the strap over the roll to compress it. **Sealed.** 0.59 L enclosed, 176 mm of usable depth. Cards ride on the outside in welded TPU slots; see §7 for why that is still an open question. ## 3. Dimensions All values below are produced by `python -m cad.build`, which writes `export/derived-dimensions.md` straight from the solid model. ### Wallet body | Feature | Dimension | | --- | --- | | Width × height | 100 × 70 mm | | Thickness, empty | 4.00 mm | | Thickness, 6 cards + cash | 7.96 mm | | Card capacity | 6–8 | The 7.96 mm figure is the sum of the layer stack (0.6 shell + 0.8 stiffener + 0.6 liner + 0.2 slot film + 4.56 cards + 1.2 cash allowance). The 12 mm in v0.1 was a guess and was 50% too thick. ### Dry bag | Feature | Dimension | | --- | --- | | Panel width (flat) | 100 mm — matches the wallet, so the roll sits flush | | Panel length (unrolled) | 280 mm | | Material consumed by the sealing roll | 104 mm | | Usable depth when sealed | 176 mm | | Cross-section, loaded | 100 × 35 mm, 14 mm corner radius | | Sealed volume | 0.59 L | | Fits | 6.9" phone (163 × 78 × 8.5), keys, cash | Panel length is **sized backwards from the phone**: 163 mm of phone plus 12 mm clearance plus the 104 mm the roll eats gives 279 mm, rounded to 280. ### Stowed envelope | Feature | Dimension | | --- | --- | | Overall, including strap | 100 × 82 × 15.2 mm | | Roll cylinder diameter | 12.4 mm | | Roll turns | 10.9 | | Target mass | ≤ 85 g | Roll diameter is verified two ways and agrees to 0.2 mm: by conservation of area (280 mm × 0.35 mm pitch spiralled around a 2.2 mm core) and by measuring the bounding box of the swept solid. ## 4. Materials and BOM | # | Part | Material | Notes | | --- | --- | --- | --- | | 1 | Bag body | 70D nylon, 0.10 mm TPU lamination both faces, ~140 g/m² | RF-weldable, must be TPU not PVC for cold-crack and recyclability | | 2 | Wallet shell | X-Pac VX21 or 210D recycled nylon with TPU face | Matte charcoal, abrasion resistant | | 3 | Wallet stiffener | 0.8 mm HDPE sheet | Encapsulated, gives the roll its batten | | 4 | Card slots | 0.2 mm clear/black TPU film | Welded, not stitched | | 5 | Lip batten | 1.5 mm semi-rigid TPU rod in welded channel | Keeps the mouth flat so the roll seals evenly | | 6 | Strap | 15 mm nylon webbing | Bar-tacked above the waterline only | | 7 | Buckle | 15 mm acetal side-release, low-profile (Duraflex Stealth class) | Matte black, no logo | | 8 | Seams | 10 mm RF-welded lap | No stitching below the fold line | Colourway: charcoal-black wallet, deep ocean blue bag, matte black hardware. ## 5. Construction sequence 1. Weld card slots to the wallet inner panel. 2. Encapsulate the HDPE stiffener between wallet outer and inner panels; weld the perimeter on three sides. 3. Weld the bag panel's top edge into the wallet's open fourth edge — this is the single critical joint and it is a continuous lap weld, never a seam. 4. Weld bag side seams, 10 mm lap, bottom corners boxed and radiused. 5. Weld the batten channel at the bag mouth, insert TPU rod, cap both ends. 6. Bar-tack the clamp strap to the wallet back face at Z=30 mm, and the buckle tab to the front face at Z=58 mm. These are the only two stitch lines. 7. Attach buckle halves; heat-seal webbing ends. ## 6. Waterproofing strategy The only stitch penetrations are the two bar-tacks that anchor the clamp strap and the buckle tab. Both sit on the wallet at Z=30 mm and Z=58 mm, well above the roll line, therefore above the waterline. Everything below is welded. Target claim: **IPX7 — 1 m submersion, 30 minutes, with 4 rolls buckled.** This is a target, not a verified rating. Validate before it goes on packaging. Test plan: - Static submersion, 1 m / 30 min, 3 and 4 rolls, tissue-paper witness inside. - Roll-count sensitivity: find the minimum rolls that hold, publish rolls + 1. - Weld peel strength on the wallet-to-bag joint, before and after cycling. - 5,000-cycle roll/unroll fatigue at the fold line — this is the likely failure point, as repeated creasing at a fixed radius will eventually craze the TPU. - Cold-crack at −20 °C. - 72 h UV exposure, check for embrittlement and colour shift. ## 7. Open risks - **Fold-line fatigue.** The bag always creases in roughly the same place. Consider a slightly softer, thinner laminate in a 20 mm band at the fold, or a deliberately varied roll start point. - **Wallet-to-bag weld.** Dissimilar materials (X-Pac face vs TPU bag) may not weld reliably. Fallback is a common TPU carrier strip welded to both. - **Stowed bulk.** 15.2 mm including the wrapped strap, 12.4 mm at the roll alone. Fine for a front pocket, tight for a back pocket. The roll diameter scales directly with panel length, so any extra depth costs bulk: the 280 mm panel needed to fit a phone already added 1 mm over the first draft. - **Cards when sealed.** They ride outside the dry volume. Acceptable if the welded slots hold, but worth prototyping a variant where the wallet inverts inward and rides inside the seal. - **Bag depth when stowed.** The 35 mm loaded cross-section is what a phone plus keys needs, but the roll maths assumes the bag flattens to two plies. Confirm on a mock-up that a 35 mm bag rolls down to 12.4 mm cleanly. ## 8. Next steps 1. Paper/tape mock-up at full scale to confirm roll diameter and the 4-roll usable depth. 2. Source a TPU laminate swatch set; run weld trials for part 3 above. 3. Soft prototype, then run the section 6 test plan. 4. Resolve the cards-outside-the-seal question before tooling the buckle. ## 9. What the CAD model changed Building `cad/` falsified four claims in v0.1. Each was caught by a test or by measuring a solid, not by opinion. | v0.1 claim | v0.2 | Why | | --- | --- | --- | | Wallet is the roll core | Wallet is the anchor plate | A 70 mm stiffened panel cannot roll into a 25 mm closure | | Panel 105 × 230 mm | 100 × 280 mm | 230 mm left 126 mm usable — a 163 mm phone did not fit. 105 mm made the roll overhang the wallet | | Loaded thickness 12 mm | 7.96 mm | Derived from the layer stack instead of guessed | | Sealed volume 1.1 L | 0.59 L | Computed on the true rounded cross-section | Unchanged and now confirmed by measurement: the 100 × 70 mm wallet, the 4.00 mm empty stack, the ~82 mm stowed height, and the roll diameter agreeing with the conservation-of-area calculation to within 0.2 mm. --- ## Renders - `renders/hero-render.png` — stowed and deployed states - `renders/construction-diagram.png` — side-profile cross-section and front elevation - `renders/deployment-sequence.png` — four-step stow → unroll → load → seal ## CAD See [`docs/cad.md`](cad.md). Build with `python -m cad.build`.