What does the H in 10H actually measure?
The H comes from the pencil hardness test, standardized as ASTM D3363 and ISO 15184. It works exactly how it sounds: a technician presses a flattened graphite pencil lead into the cured coating at a 45-degree angle and pushes it across the surface in a short stroke. Pencil grades run from 9B (softest) up through H grades (hardest). The coating's rating is the hardest pencil that fails to gouge or visibly mar the film.
Standard ASTM test sets top out at 9H. A few pencil manufacturers produce a 10H grade lead, which is where 10H ratings come from — the coating resisted the hardest graphite pencil its maker could buy. It is a legitimate lab test, originally designed for quality control on industrial paint films, and it does tell you something real about film density and cure.
What it is not is the Mohs scale. Mohs measures mineral hardness from talc (1) to diamond (10), and marketing frequently blurs the two. A coating that passes a 9H pencil sits somewhere around 2 to 3 on Mohs by most published estimates — well below the quartz (Mohs 7) that makes up much of road dust and sand. If a coating were truly a 9 on Mohs, a dried sample would scratch glass. None do.
What don't 9H and 10H claims tell you?
They don't tell you the coating is scratch-proof. The test object is graphite. The things that scratch cars are steel keys, gravel, grit-loaded wash mitts, and quartz sand — all dramatically harder than any pencil lead. A 10H coating can ace the lab test and still pick up a scratch from a careless fingernail loaded with dust.
They also can't reliably split hairs between similar products. ASTM's own guidance notes that pencil test results vary between labs, pencil brands, and substrates, and that the method is best for ranking coatings with significant hardness differences. The gap between 9H and 10H is a single pencil grade at the very top of the scale — close to the noise floor of the test itself.
Finally, these numbers are self-reported by manufacturers, with no independent body auditing consumer claims. When you see ratings like 12H or 20H, be skeptical: no standard test pencil exists at those grades, so there is no test the number could have come from.
Will a 10H coating stop scratches on your car?
It will meaningfully reduce the most common kind: wash-induced marring. Most visible paint damage on daily drivers is swirl marks from washing and drying. A hard, slick ceramic surface lets wash media glide instead of drag, and dirt releases with less pressure, so you inflict fewer micro-scratches every time you clean the car. Add strong chemical resistance and UV protection, and that is the honest value of a quality coating.
It will not stop rock chips, key scratches, or scrapes. A ceramic coating is roughly 1 to 3 microns thick — a fraction of the clear coat beneath it, which measures in the tens of microns. No film that thin absorbs the impact energy of a stone at highway speed, regardless of its pencil rating.
If impact protection is the goal, that is paint protection film (PPF) territory — a urethane film thick enough to absorb chips. Some installers combine the two; DetailPros' Flagship package ($1,399), for example, pairs a full ceramic coating with PPF on impact zones for exactly this reason. Coating for chemistry and wash protection, film for impacts.
What actually determines how long a coating lasts?
Chemistry first. SiO2 (silicon dioxide) content varies enormously: consumer spray coatings commonly run 5 to 15 percent, while professional-grade coatings carry far higher solids. Higher SiO2 concentration generally means a denser cross-linked film and longer service life — which is why pro coatings are quoted in years and spray sealants in months.
Curing second. Most coatings reach an initial cure in 24 to 48 hours but need two to three weeks to fully cross-link. Getting the car rained on, washed, or coated in dew during that window compromises the film. Temperature and humidity during application matter too, which is why installers care about conditions, not just product.
Bonding third — and this is where jobs actually fail. A coating only performs on a surface it has chemically bonded to. Leftover iron particles, embedded contamination, polishing oils, or old wax under the coating create weak points that flake and fail early. In other words: the number on the bottle sets the ceiling, and prep decides whether you get anywhere near it.
Why does prep matter more than the number on the bottle?
Because ceramic coatings are optically clear and microns thin, they hide nothing. Whatever condition your paint is in when the coating goes on — swirls, oxidation, water spots — gets locked under a glossy, semi-permanent layer. A cheap coating over corrected paint will look better and last longer than a premium 10H coating slapped over contaminated, swirled clear coat.
Proper prep is a sequence, not a step: iron decontamination to dissolve embedded brake dust, clay bar to pull bonded contaminants, machine polishing to level swirls and restore gloss, and an IPA (alcohol) wipe-down to strip polishing oils so the coating bonds to bare clear coat. Skipping any one of these weakens the result.
This is also where real-world pricing comes from. As one data point, DetailPros includes all four prep steps — iron decon, clay bar, single-stage machine polish, IPA wipe — in every ceramic package starting at $599, with two-step correction added at the $899 tier. Standalone correction runs $199 for one-step and $399 for two-step, assessed with a paint depth gauge. Whoever you hire, ask them to itemize their prep; an installer who can't list these steps is selling you the bottle, not the result.
What is McKee's 37 10H, and how should you read the rating?
McKee's 37 Paint Coating is an SiO2-based ceramic that uses nano-glass ceramic particles and cross-linking polymers to form a hard, hydrophobic film on clear coat. Its 10H rating means the cured film resisted the hardest available test pencil — a genuine indicator of a dense, fully cross-linked film, read the way this guide describes: a lab film-hardness result, not a scratch-proof promise.
DetailPros installs McKee's 37 as its coating line across the Las Vegas Valley and Southwest Florida (Punta Gorda, Cape Coral, Fort Myers, Naples, Port Charlotte), fully mobile, with 5-year protection and packages from $599. The 5-year figure comes from the full system — decontamination, correction, coating, cure guidance — not the H number alone.
Wherever you buy, evaluate the installer, not just the chemistry: itemized prep steps, aftercare instructions for the cure window, and something backing the work. For reference, DetailPros carries a 7-Day Redo Guarantee and $2M liability insurance, and takes a $50 deposit that applies to the invoice — reasonable benchmarks to hold any shop or mobile outfit against.