Topre & EC Dome Force Curves: How to Read and Compare Domes

Every dome you can buy is sold under a single number. Topre 45g. Deskeys v2 49g. DynaCaps Medium. Astro Domes 70g. That number is, in almost every case, nothing more than the dome's measured collapse force — the force at the tactile peak. It's one point on a curve, and your fingers feel the entire stroke. Two domes with similar ratings can feel completely different, and a dome that collapses at a higher force than a Topre 45g can still feel lighter under your fingers. The rating system isn't wrong, exactly — it's just nowhere near enough.

So I had a force bench built, measured every dome I could get on it, and published the results as an interactive tool: the Topre Force Curve Bench. This post explains the hardware, what's measured, how, and why the two numbers at the center of it — Total Energy and Snap % — are the correct way to compare domes.

The bench

The Open-Switch-Curve-Meter (Gen 2) — designed by bluepylons. Photo by bluepylons, from the project's GitHub repository.

Credit where it belongs: the measurement rig is a build of the Open-Switch-Curve-Meter, an open-source force-curve measurement device designed and published by bluepylons. Every number on this page exists because that design exists.

My unit was commissioned as a custom build from a third-party professional — a machine with stepper-driven displacement, load-cell instrumentation, and calibration requirements is worth having assembled by an expert, and that expertise shows up directly in the repeatability of the data below. To be completely clear about who did what: the fabricator built it to order, and skillfully; the design is 100% bluepylons' open-source work, not theirs.

The two numbers that actually compare domes

Total Energy (gf·mm) answers: how heavy is this dome, actually? It's the area under the press curve from the start of the stroke to bottom-out — the total work your finger does across the whole keystroke. Because it accounts for the entire stroke rather than one point on it, it's the honest single number for weight. This is how a Deskeys dome rated heavier than a Topre can measure — and feel — lighter overall.

Snap % answers: how tactile is it? It's the percentage drop from the collapse peak to the post-collapse minimum: (Collapse − Valley) / Collapse × 100. This isn't something I invented — it's the dome-switch industry's tactile-ratio standard. A linear switch scores 0%. A stock Topre 45g lands around 14%. BKE Redux Extreme, the most tactile dome I've measured, reaches the high 50s.

Neither of these numbers is published by any dome maker or measured anywhere else for Topre-compatible parts. That's the gap this project fills.

How the measurements are made

The bench steps displacement in 0.005 mm increments — quasi-static, about 0.15 mm/s — while logging force from a load cell calibrated and verified against standardized test weights. Each configuration is tested in multiple runs and averaged. Run-to-run deviation in collapse force is under one gram, which is why I publish grams and gf·mm as whole numbers: the precision shown matches the precision that exists.

From the averaged press curve, five values are read:

• Collapse Force / Collapse Travel — the tactile peak: how hard, and how far into the stroke, the dome buckles. This is the closest thing to the "weight" printed on the box.
• Valley — the post-collapse minimum, used to compute Snap %.
• Travel — where the bottom-out wall begins, detected where the press slope exceeds 300 g/mm past the valley. Dome bottom-out walls are near-vertical, so this detection is robust.
• Total Energy — the press curve integrated from 0 to Travel, in gf·mm.
• Snap % — (Collapse − Valley) / Collapse × 100.

Reference results

Test set	Collapse (g @ mm)	Snap %	Travel (mm)	Total Energy (gf·mm)
Topre 30g	36 @ 0.69	25	3.99	131
Topre 45g	52 @ 1.30	14	3.96	178
Topre 55g	64 @ 1.25	20	3.95	213
Topre 55g (aged)	70 @ 1.05	23	3.98	224
NiZ 65g	76 @ 1.66	13	3.94	251
BKE Redux Extreme	132 @ 0.95	57	3.32	311
DynaCaps Light	44 @ 1.19	16	4.10	158
DynaCaps Medium	49 @ 1.15	18	4.02	173
DynaCaps Heavy	53 @ 1.11	20	4.00	185
Topre Slider Black (bare)	63 @ 1.13	23	3.99	207
+ 0.3 mm poron ring	61 @ 0.98	24	3.75	196
+ 0.5 mm poron ring	68 @ 0.79	25	3.62	207

A few things worth pulling out of that table. The "aged" Topre 55g set measures a noticeably higher collapse force than fresh 55g domes — age matters, and it's part of why old HHKB Pro 2 boards sold as 45g can test far heavier. And look at Topre 45g vs. DynaCaps Medium: nearly identical Total Energy (178 vs. 173 gf·mm), meaning they're genuinely comparable in weight — something their names alone would never tell you.

What silencing rings actually do

The same slider, three silencing configurations, measured. Chart: Unreal Keyboards dome lab.

First, the mechanism — because it explains everything in the chart. Per Topre's own silencing patent (JP2012-138254A) and CAD sections of the real parts, a silencing ring rides on top of the slider, around its keycap tube, and does its work on the upstroke: the ring lands on the housing's stop wall so rubber strikes instead of plastic. On a standard slider that thickness has nowhere to go, so it preloads the dome at rest. Topre's factory silent sliders carry a ~0.5 mm recess that exactly absorbs their factory ring — silenced with zero preload and full travel — which is precisely the trade an aftermarket ring on a standard slider can't make. The data:

Travel loss ≈ ring thickness, less for poron. The 0.5 mm poron ring removed 0.37 mm of travel — foam absorbs part of its own thickness under preload. Silicone transmits closer to its full thickness.

The collapse point arrives earlier by roughly the ring's effective thickness. The preloaded dome starts the measured stroke partway up its intrinsic curve — you can see it in the data as an elevated force reading in the first hundredths of a millimeter.

Measured collapse force goes up, not down. This is the counterintuitive one. Preload alone can't explain it — a pure preload just moves you along the same curve. The increase means the ring changes the dome's intrinsic buckling load, which is consistent with how shell buckling works: the critical snap-through force is highly sensitive to how the load is distributed, and a ring loads the dome crown through a wider footprint than the slider's native contact.

Slow-press tactility barely changes — felt tactility does. Snap % is nearly identical bare vs. 0.5 mm ring on the bench, yet thick rings feel markedly less tactile when typing. The difference is speed: the bench presses quasi-statically, while a keystroke moves orders of magnitude faster, where foam damps the snap transient. This is exactly why Snap % should be read alongside Collapse Travel and Travel whenever rings are involved — and why up to a 0.3 mm poron ring the feel survives largely intact, while a standard 0.5 mm drastically dulls it.

See the mechanism move

If you want to watch all of this happen instead of reading it, I built an interactive cross-section of the complete switch: the EC Switch Explorer. Its geometry is traced 1:1 from CAD of the real parts, its dome collapses using the measured curves from this bench, and you can swap sliders and rings and watch the preload, the snap, and the top-out rattle appear in front of you.

Explore the data yourself

The interactive bench lets you overlay any combination of these tests, read exact values off the curves, and export publication-ready charts. Every raw CSV — full press and return strokes at 0.005 mm resolution — is public in the GitHub repository, and new tests appear in the bench automatically as they're pushed. Exported charts and data may be shared with attribution and a link back.

This is an ongoing project. More domes, more silencing configurations, and a deeper dive into the mechanics of dome collapse are coming.

Image credits: bench photo by bluepylons, from the Open-Switch-Curve-Meter repository; force-curve chart by Unreal Keyboards.

© 2026 Brian "BuddyOG" Gebo — Unreal Keyboards. All rights reserved.