Most people buying a watch strap never look at the durometer spec. That's fine — until you've owned a strap so stiff it left marks on your wrist, or so soft it stretched out of shape by lunch.
Shore A hardness is the number that separates those two failures. Here's what it means, how to read it, and why we chose Shore A 50 for POPSTRAP.
What Is Shore A Hardness?
Shore hardness is a standardized scale for measuring a material's resistance to permanent indentation. Developed by Albert Ferdinand Shore in the 1920s, it remains the industry benchmark for flexible polymers — rubber, silicone, foam, elastomers.
The "A" refers to the specific indenter geometry used for soft, flexible materials. (Shore D is for rigid plastics; Shore OO covers very soft gels.) When you see a silicone product spec'd at Shore A 50, it means a standardized needle pressed with a defined force left an indentation reading 50 on a 0–100 scale.
Lower number = softer. Higher number = harder. Simple as that.
The Scale in Practice
To make that number tangible:
| Shore A | Feel | Real-world example |
|---|---|---|
| 10–20 | Very soft, gel-like | Medical implant silicone, silicone sealant |
| 30–40 | Soft, pliable | Baby pacifier, earbud tips |
| 50–60 | Medium, structured flex | POPSTRAP, quality dive straps |
| 70–80 | Firm with slight give | Shoe sole, hockey puck |
| 90–100 | Near-rigid | Hard eraser, tool grips |
A strap at Shore A 30 will feel buttery soft out of the box — but it deforms at the buckle holes, stretches under a heavy watch head, and loses its geometry fast. At Shore A 80, the strap holds its shape perfectly but clamps the wrist and resists conforming to the skin. You feel every edge after an hour.
The 50–60 zone is the practical sweet spot for daily-wear straps that need both structural integrity and skin compliance. Not soft enough to collapse, not hard enough to punish.
Why POPSTRAP Runs at Shore A 50
POPSTRAP is a cage strap. That means defined rails, precise cut-outs, and a geometry that has to survive thousands of buckle cycles and the lateral stress a 40mm watch head puts on the strap during active wear. Structure is not optional.
Shore A 50 gives us two things at once:
Structural memory. The strap snaps back. The cage cut-outs don't deform under wrist pressure. The buckle holes stay round after a year of daily use. The geometry you see on the product page is the geometry you'll have twelve months later.
Wrist compliance. At Shore A 50, the silicone still conforms to the wrist profile without fighting it. The inner surface sits flat against the skin rather than bridging over it. You don't feel sharp inner edges working against you on a long day.
Going harder would have given us a crisper cage — cleaner off a mold, but a punishing wear experience. Going softer would have collapsed the rails over time. Shore A 50 isn't a compromise. It's the right answer for a structured strap worn all day, every day. Learn more about how we approach material selection on our workshop page.
Shore A and Durability: What the Number Doesn't Tell You
Hardness and tear strength are related but independent. A Shore A 50 silicone can be significantly tougher than a Shore A 70 silicone depending on its base polymer, cure chemistry, and cross-link density.
What hardness does affect is fatigue resistance at high-flex zones — buckle hole edges, cage hinge points, anywhere the material bends and recovers on every wear cycle. Softer silicones yield more per cycle. Over 300+ buckle cycles a year, cumulative micro-deformation compounds.
POPSTRAP uses platinum-cured silicone with a high cross-link density. That means our Shore A 50 is backed by a polymer network built to resist micro-fatigue at stress points — not just a number on a spec sheet. For a deeper look at why cure chemistry matters, see our Silicone Strap Guide.
How to Read Shore A When Buying Any Strap
Spec sheets don't always list Shore A. When they do, here's the quick read:
- Under Shore A 40: fine for dress straps worn occasionally. Not suited for structured cage designs or high-activity wear.
- Shore A 40–55: the performance window. Flexible enough for comfort, firm enough to hold form. This is where quality aftermarket straps live.
- Shore A 60 and above: dive and expedition straps built for extreme conditions. More rigid on the wrist, more resistant to compression.
If a brand doesn't publish the durometer, ask. If they can't answer, that's information too. Material transparency is a baseline, not a differentiator.
POPSTRAP publishes its full spec — Shore A 50, platinum-cured, medical-grade silicone, made in Loiret, France. If you want to feel what the right number feels like on a wrist, start with Drop 01.