Photo: Purple Mountain Observatory
A shoe upper is normally an assembly — panels cut, stitched, glued, lined. The Calyx deletes the assembly: one sheet of rubber, moulded in a single piece, waterproof because there is no seam for water to find.
Verdict
| What it is | Purple Mountain Observatory Calyx™ in Stone — a slip-on camp shoe whose upper is moulded from a single sheet of rubber (Vibram StratX), closed by a knit collar and carried on a Vibram Grivola outsole in Megagrip compound |
| Price | £150 — Purple Mountain Observatory's own store, checked Tue Nov 10, 2026; the same price across all five colourways |
| Availability | On sale now at the maker's store and select retailers. Five colourways — Stone, Gray, Black, Green, Brown — in EU sizes 37–46 |
| The angle | The waterproof shoe's usual failure points — seams, stitching, layered panels — removed by construction rather than sealed after the fact |
| Verdict | A camp shoe rebuilt as a sealed shell. The interesting thing about the Calyx is not that it keeps water out, but how little of a shoe there is to let it in. |
What it is
Purple Mountain Observatory is a small London label founded by Matt Braun, and the Calyx is its debut footwear silhouette — a modern reading of the classic camp shoe, made in collaboration with Vibram and pitched, in the brand's words, at “the moments between effort and recovery.”
The upper is sculpted from a single sheet of specialised rubber using Vibram's StratX formula — the maker's own description is that it eliminates “the need for traditional stitching or layering.” There are no panels and no seams anywhere on the shell. The only textile is the ribbed knit collar that closes around the ankle, with a webbing pull tab at the heel; the process itself is debossed on the quarter, a small Vibram StratX mark printed into the rubber. Underneath sits the Vibram Grivola outsole, its Megagrip compound there for lightweight grip on wet and dry ground alike.
The Calyx first launched in 2025. This second run — on sale since Oct 29, 2026 — adds new colourways and updated sole treatments. Stone, pictured here, is the olive-toned colourway: bone sole, dark olive collar, black heel tab. All five colourways are £150.
Why it matters
Most waterproof shoes are ordinary shoes plus defences — a membrane, seam tape, a coating — and each defence is a layer that can split, clog or wear through. The Calyx takes the other route: a single moulded shell has no stitch holes to wick, no panels to delaminate, nothing glued along a flex line. It is the camp shoe — the loose slip-on meant for the ground between the trail and the tent — rebuilt over a lugged trail sole, which is also what makes it a city shoe: sealed against the weather, grippy underneath, nothing to lace.
Specs
| Brand | Purple Mountain Observatory (London, founded by Matt Braun) |
| Model | Calyx™ — featured colourway Stone |
| Upper | Single sheet of rubber, moulded via Vibram StratX — seamless, waterproof; no stitching or layering |
| Collar | Ribbed knit collar, webbing heel pull tab |
| Outsole | Vibram Grivola, Megagrip compound |
| Colourways | Stone, Gray, Black, Green, Brown |
| Sizes | EU 37–46 |
| Price | £150 at the maker's store |
What to check before buying
- Sizing is EU-only, with no half sizes. The listing runs 37–46, and a slip-on has no laces to correct a loose heel — the knit collar is the whole fit system, so get the length right.
- No weight is published. The maker's listing gives no weight figure; judge the shoe by its construction — a full rubber shell over a lugged trail sole — or in hand.
- Buy at the source. The £150 price is the maker's own, from Purple Mountain Observatory's store; the Calyx also appears in select retailers' catalogues.
Price record
| Price | £150 |
| Source | Purple Mountain Observatory's own store (purplemountainobservatory.co.uk) — checked Tue Nov 10, 2026; £150 across all five colourways |
| Featured | Site-first, Tue Nov 10, 2026 — the Instagram post follows in Saturday's Trail & Approach carousel |
Want one?
- In the shop: browse current stock — one-off pieces, and they turn over fast.
- Hunting one? Join the Want List — tell us the maker and the budget; pieces like this surface in our trawl most weeks.
- This one: at the source — See it at Purple Mountain Observatory. Not our listing. See Disclosure.
Related picks
- The North Face Clyffe Slip-On — the approach shoe, minus the laces, at $140
- Reebok × A Herd of Bison Trailzillo DMX — a trail shoe with a compass on the tongue, at $130
- PANE Dyno Step — a bouldering sole, bolted on in sections, price not published
Spotted, not sold by us — this shoe lives at Purple Mountain Observatory. Prices are a snapshot from when we spotted it. Disclosure
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Shop the pick
Purple Mountain Observatory Calyx™ — Stone
£150 — Purple Mountain Observatory, checked Tue Nov 10, 2026
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