Flooring marketing runs on numbers most buyers have never had explained: mils, AC classes, PEI, Janka, density, DCOF, CSP. Here is what each one measures, what number you actually need, and which ones are meaningful versus decorative.
Five groups of specification, from wear ratings to acoustics. These are the numbers on the sample board that nobody explains at the counter.
The clear film on top of an LVP or LVT plank, measured in mils (thousandths of an inch). It is the only thing between traffic and the printed image, and it is the single strongest predictor of how long a vinyl floor keeps looking new.
| 6 mil | Light residential, rental-grade. Visible wear in 3–5 years in a busy home. |
|---|---|
| 12 mil | The residential sweet spot. Handles pets, kids and daily traffic. |
| 20 mil | Light-to-general commercial. The correct spec for retail and offices. |
| 28–30 mil | Heavy commercial. Airports, hospitals, high-traffic retail. |
Note: a 6 mil and a 20 mil plank can look and feel identical in the store. Total plank thickness tells you nothing about the wear layer.
The Abrasion Class from the European EN 13329 standard, established by a rotating abrasive wheel test. Higher numbers survive more revolutions before the decorative layer wears through.
| AC1 | Moderate residential — closets, bedrooms only |
|---|---|
| AC2 | General residential — light traffic |
| AC3 | Heavy residential / moderate commercial — ≥2,500 cycles, the common retail grade |
| AC4 | General commercial — ≥4,000 cycles, recommended for any busy household |
| AC5 | Heavy commercial — ≥6,500 cycles, retail floors, public corridors |
| AC6 | Above AC5; uncommon in residential retail |
The cost difference between AC3 and AC4 is usually well under a dollar per square foot. Take the upgrade. Note that AC is a European classification adopted into North American marketing — NALFA LF-01, the North American standard, certifies to its own levels and does not use AC numbers.
Porcelain Enamel Institute classification for surface wear on glazed tile, based on how many revolutions of abrasive it withstands before visible change.
Unglazed and through-body porcelain is not assigned a PEI class because there is no glaze to wear through — it is rated instead on abrasion resistance of the body.
Pounds of force required to embed a 0.444" steel ball halfway into a wood sample. It predicts denting, not scratching — a hard wood with a soft finish still scratches easily.
| Brazilian cherry | 2,350 |
|---|---|
| Hickory | 1,820 |
| Hard maple | 1,450 |
| White oak | 1,360 |
| Red oak (reference) | 1,290 |
| Walnut | 1,010 |
| Douglas fir | 660 |
| Eastern white pine | 380 |
Density is the number that actually predicts carpet life: face weight ÷ pile height × 36. Above 3,000 is solid residential; above 5,000 is commercial-grade.
Twist level (turns per inch) determines whether traffic lanes "bloom" into a fuzzy, permanently dirty-looking appearance. Look for 5+ TPI on frieze and confirm the yarn is heat-set.
Practical test in the showroom: bend a sample back on itself. If you can easily see the backing through the fibers, density is low. This is called "grinning."
Dynamic Coefficient of Friction. ANSI A137.1 requires 0.42 or greater for tile recommended for level interior floors expected to be walked on when wet, measured by the DCOF AcuTest per ANSI A326.3.
Polished porcelain and polished stone routinely test below this and should not be used in showers, entries, pool surrounds or commercial kitchens. Texture, small format with more grout lines, and honed or tumbled finishes all raise effective traction.
0.42 is a minimum for level interior floors, not a universal pass mark. Ramps, wet-process areas and exterior applications require more.
SPC (stone-plastic composite) — limestone powder plus PVC, extruded dense and rigid. Thin, dent-resistant, dimensionally stable, cheaper. Harder and louder underfoot; telegraphs subfloor bumps.
WPC (wood-plastic composite) — foamed core with wood flour. Thicker, warmer, quieter, softer, better over slightly imperfect substrates. Dents under sustained point loads.
Both are 100% waterproof. Neither contains lumber that can rot — the "wood" in WPC is encapsulated flour.
A wear layer of real hardwood over a cross-ply or HDF core. The cross-grain construction is what stops seasonal movement and makes slab and radiant installations possible.
Sawn-face veneer looks like solid wood. Rotary-peeled veneer is unwound from the log and repeats a plywood-like figure.
Solution-dyed means pigment was added before extrusion. It is the single most valuable durability upgrade in any synthetic carpet.
Sanded grout is for joints 1/8" and wider; unsanded for narrower joints where sand would not fit. Neither grout type is what makes a shower waterproof — that is the membrane beneath.
Water absorption defines the categories: non-vitreous above 7%, semi-vitreous 3–7%, vitreous 0.5–3%, and impervious (porcelain) at or below 0.5%.
Absorption determines freeze-thaw survival, which is why porcelain works outdoors in cold climates and standard ceramic does not. Rectified tile has been mechanically ground to exact dimensions, enabling 1/16" grout joints; non-rectified needs wider joints to absorb size variance.
Lithium, sodium or potassium silicate penetrates a concrete slab and reacts with free calcium hydroxide to form additional binder — hardening the surface from within rather than coating it.
Polishing then runs progressively finer diamond abrasives, from roughly 30 grit up to 1500–3000 for a mirror finish. Because there is no coating, there is nothing to peel, and the floor can be reground indefinitely.
Every floating floor needs 1/4"–3/8" of free space at every wall, pipe, column and door jamb, hidden under baseboard or trim. Vinyl and laminate expand with temperature and humidity; if the movement has nowhere to go, the floor peaks in the middle or the joints separate.
An installer runs the floor tight to a wall or under a heavy kitchen island that pins it. The floor buckles months later and gets blamed on the product.
Wood must sit in the actual installation space, boxes opened, until moisture content equilibrates — NWFA guidance allows no more than 4% difference between flooring and subfloor for solid strip, and 2% for plank wider than 3 inches. Typically 3–7 days; longer in extreme climates.
Target 6–9% equilibrium moisture content, which corresponds to the NWFA's recommended 30–50% relative humidity at 60–80 °F. Vinyl needs 24–48 hours at service temperature. Skipping acclimation produces gaps in winter, cupping in summer, and voided warranties year-round.
Concrete releases vapor for months after placement, and a slab without an intact vapor retarder never stops. ASTM F2170 in-situ relative humidity probes are the current standard; ASTM F1869 calcium chloride is the older surface method.
F2170 caps in-slab RH at 75% and F1869 caps emission at 3 lbs/1,000 sq ft/24 hr unless the flooring or adhesive manufacturer states otherwise; some products are warranted to 80–85%. Above the stated limit a moisture-mitigation system is required — budget $1.50–$5.00 per square foot rather than discovering it mid-project.
A dimpled polyethylene or fabric layer between substrate and tile that lets the two move independently. Substrates expand, contract and deflect; tile does not. Without a separation layer, that movement transfers straight into the tile and grout as cracks.
Standard practice over any wood subfloor, and increasingly over slabs with control joints. It also provides a degree of waterproofing and, in some products, a channel for radiant heat cable.
Over concrete, a 6-mil vapor barrier is required beneath any floating floor whether or not the underlayment claims to include one.
Ask for a current certificate tied to the specific SKU. Category claims on a website are not the same as a product certificate.
The floor covering is often not the largest contributor. Adhesives, seam sealers, finishes and underlayments frequently emit more than the product they install. Specify low-VOC across the whole assembly, not just the visible layer.
New installations off-gas most in the first 48–72 hours. Ventilate aggressively during and after, and schedule installation ahead of occupancy where possible.
The old advice to remove all carpet for allergy sufferers is more nuanced than it was. Carpet traps particulate and holds it out of the breathing zone until vacuumed; hard surfaces let it re-aerosolize with every footstep.
The practical determinant is maintenance. A frequently vacuumed carpet with a HEPA-filtered machine can perform well; a neglected one is a reservoir. Hard surface plus washable rugs is the lower-effort path to the same outcome.
If avoiding PVC is a project requirement, the workable categories are linoleum, wood, tile, stone, terrazzo, polished concrete, wool and PET carpet, and PVC-free-backed carpet tile.
The category that has to go is vinyl in all its forms — LVP, LVT, SPC, WPC, VCT and sheet vinyl are all polyvinyl chloride.
Look for a third-party program with published criteria: an Environmental Product Declaration (EPD), a Health Product Declaration (HPD), Declare labels, Cradle to Cradle certification, or FSC for wood.
Unverified terms like "eco-friendly," "green" and "natural" have no defined meaning in flooring and appear on products with very different profiles.
IIC (Impact Insulation Class) measures footfall and dropped-object noise transmitted downward through the floor-ceiling assembly. STC (Sound Transmission Class) measures airborne sound — voices, television.
The International Building Code sets a minimum of 50 for both between dwelling units when laboratory tested, or 45 when field tested. Many condo boards and hotel brands require 55–60, and a hard-surface installation in a condo often needs specific board approval before work begins.
An underlayment advertised at "IIC 70" was tested in a specific concrete assembly. Over wood framing the same product can perform 15–20 points lower. Ask for the tested assembly, not the headline number.
A floating floor over a thin foam pad produces a distinctive hollow click. Cork or rubber underlayment, or glue-down installation, removes it.
Carpet is the warmest surface underfoot; tile, stone and concrete are the coldest. Wood and WPC vinyl sit in between; SPC is noticeably colder than WPC because its dense core conducts heat away faster.
Under radiant heat the ranking inverts — tile and stone are the best conductors and deliver the most heat into the room, while carpet insulates against the system it sits on.
Surface temperature should stay below 80–85 °F for nearly all products, and temperature changes should be ramped slowly — sudden swings cause more damage than heat.
If people stand in one place for long periods — a kitchen, a lab bench, a checkout counter, a workshop — the floor's give matters more than any other property.
Carpet reduces fatigue meaningfully. Vinyl and linoleum are moderate. Tile, stone and concrete provide none, which is why anti-fatigue mats are standard equipment on hard floors in professional kitchens.
IIC and STC describe sound leaving the room. Reverberation inside it is a separate problem — hard surfaces reflect sound and make rooms feel loud and speech hard to follow.
This matters most in open offices, restaurants, classrooms and open-plan homes. Carpet and carpet tile absorb; area rugs, upholstery and acoustic ceilings do the same job when the floor cannot.
Every term used on this site, defined plainly.
Abrasion Class for laminate under EN 13329, AC1–AC6, in Taber cycles: AC3 ≥2,500 (heavy domestic), AC4 ≥4,000 (general commercial), AC5 ≥6,500 (heavy commercial). A European classification adopted into North American marketing; NALFA LF-01 certifies to its own levels instead. Buy AC4+ for a busy household.
Porcelain Enamel Institute surface-wear class for glazed tile, 1–5. Class 4 or higher for residential floors that see real traffic.
Thickness of the clear protective film on vinyl. 6 mil = light residential, 12 mil = active household, 20–30 mil = commercial. One mil = 1/1000 inch.
Pound-force required to embed a 0.444-inch steel ball halfway into the wood. Red oak = 1,290 is the North American reference. Below 1,000 dents visibly in active homes. Values far above 3,000 are outside the range the test was calibrated for and compress.
Dynamic Coefficient of Friction. ANSI A137.1 requires ≥0.42 wet for tile recommended for level interior floors walked on when wet, tested by the DCOF AcuTest per ANSI A326.3. A minimum threshold, not a guarantee of suitability. Polished stone and tile frequently fail it.
Average pile yarn density = face weight × 36 ÷ pile height, in oz/yd³. Results typically fall between 1,000 and 7,000; CRI recommends 5,000 or higher for extra-heavy traffic. A better predictor of life than face weight alone.
Ounces of fiber per square yard of carpet face. Useful only alongside pile height and density — a high face weight with tall pile can still crush.
Turns per inch in the yarn. Higher twist, heat-set, resists the untwisting that makes traffic lanes look permanently soiled.
Pigment added to liquid polymer before extrusion, so color runs through the fiber. Effectively bleach-proof and fade-proof.
Stone-plastic composite (rigid, dent-resistant, thin, cheaper) versus wood-plastic composite (foamed, warmer, quieter, softer, dents more).
Surface texture physically aligned with the printed grain pattern. The main thing separating convincing laminate/LVP from obviously artificial product.
Tile mechanically ground to exact dimensions, allowing 1/16" grout joints. Non-rectified tile needs wider joints to absorb size variance.
A layer between substrate and tile that absorbs substrate movement. The standard defense against cracked tile and grout over wood subfloors.
Height difference between adjacent tile edges. The enemy of large-format installs — controlled by substrate flatness and leveling clip systems.
Resin-based grout that is waterproof and stain-proof and never needs sealing. Higher cost and harder to install than cement grout.
A stain is absorbed material (removable with a poultice). An etch is dissolved surface from acid contact (requires re-polishing). Sealer stops stains, not etching.
Calcium-carbonate stones — marble, limestone, travertine, onyx — that react with acid. Siliceous stones like granite and slate do not.
Penetrating sealer that sits below the surface without changing appearance. Preferred over topical sealers, which wear and must be stripped.
Moisture vapor emission rate (ASTM F1869, ≤3 lbs/1,000 sq ft/24 hr) and in-situ relative humidity (ASTM F2170, ≤75% unless the manufacturer allows more). Required before any glue-down or vapor-impermeable floor over concrete.
ICRI 310.2R scale 1–10 describing concrete roughness after preparation. Thin sealers bond at CSP 1–2, high-build epoxy and urethane at CSP 3–5, polymer overlays at CSP 6+. Achieved by grinding or shot blasting, not acid etching.
Storing flooring in the installed space until its moisture content equilibrates with the room. NWFA allows no more than 4% difference between flooring and subfloor for solid strip, 2% for plank over 3 inches wide, at 30–50% RH and 60–80 °F. Skipping it is the leading cause of gapping and cupping.
The 1/4"–3/8" perimeter space a floating floor needs to move. Blocked expansion gaps cause peaking, buckling and joint separation.
A floor that locks to itself but is not fastened to the subfloor. Fast and DIY-friendly; requires a flat substrate and strict expansion gaps.
The layer between subfloor and floor. Controls acoustics, moisture, comfort and minor substrate irregularity. Often the cheapest meaningful upgrade available.
Impact Insulation Class (footfall transmitted downward, ASTM E492) and Sound Transmission Class (airborne, ASTM E90). IBC requires 50 laboratory-tested between dwelling units, or 45 field-tested; condo boards often require 55–60 for hard surface.
Third-party certifications for low VOC emissions and indoor air quality. Worth requiring by name in any spec, residential or commercial.
Formaldehyde emission limits for composite wood cores. Applies to laminate and engineered wood cores. Ask for documentation on imported product.
Surplus material — 5% is the standard order — stored on site after installation. A tile or plank replaced years later from attic stock matches, because it came from the same production run. Buying a replacement later almost never matches the dye lot.
Subfloor imperfections showing through the finished floor as visible ridges, dips or shadows. Thin resilient sheet and large-format tile telegraph the most; thick carpet cushion and rigid cores hide more. It is a preparation failure, not a product defect.
Installed cost plus maintenance plus replacement across a defined period. The number that reverses most "cheapest option" decisions — see VCT versus LVT.