Tile Terms 101: What Those Specs Are Actually Telling You

We know tile isn't the most exciting thing you could be educating yourself about, and  shopping for tile can feel like reading a foreign language. Rectified. Vitreous. V3. PEI 4. DCOF 0.42. It's easy to assume it's all technical noise invented to make a simple purchase complicated. 

It isn't. Nearly every one of those terms describes a real, measurable property that determines whether your floor still looks beautiful in ten years or starts showing wear in two. The problem isn't that the terminology is useless — it's that almost nobody translates it for you.

So here's the translation. This is the vocabulary you'll see on spec sheets and product pages, explained in plain English, organized around the decisions you're actually making.

Porcelain vs. Ceramic: It Comes Down To One Number

This is the most misunderstood distinction in the entire tile industry, and it's worth getting right because it drives so much else.

Porcelain is ceramic. It's not a separate material — it's a subcategory of ceramic tile, and it's defined by exactly one measurable property: how much water the tile body absorbs.

Under the ANSI A137.1 standard, a tile qualifies as porcelain if it absorbs 0.5% or less of its own weight in water when tested per ASTM C373. Above that threshold, it's non-porcelain ceramic. That's the whole definition. It's not about price, prestige, or appearance.

That single number, though, cascades into real differences:

	Porcelain	Ceramic (non-porcelain)
Water absorption	0.5% or less	More than 0.5%
Body density	Denser, fired hotter and longer	Slightly more porous
Freeze/thaw	Suitable for exterior use	Interior use only
Installation	Harder — needs quality blades and the right mortar	Easier to cut and handle
Best for	Floors, wet areas, exteriors, heavy traffic	Walls, backsplashes, light-traffic floors

Here's the part that surprises people: porcelain isn't automatically the better choice. It's denser and more water-resistant, which matters enormously in a shower or an entryway and matters very little on a kitchen backsplash three feet above a countertop. Ceramic bodies also take glaze beautifully, which is why so many of the richest colors and most characterful handmade-look tiles are ceramic. You'll often get more visual personality per dollar.

Match the material to the job. For a shower floor, a mudroom, or a covered patio, specify porcelain. For a backsplash or a powder room feature wall, choose whatever looks right.

One related term you may see: tile is sometimes classified by absorption as impervious (0.5% or less), vitreous (0.5–3%), semi-vitreous (3–7%), or non-vitreous (over 7%). Same idea, finer gradations. Impervious and porcelain mean the same thing.

Rectified vs. Non-Rectified: This Is A Grout Joint Decision

Tile shrinks when it's fired, and it doesn't shrink perfectly evenly. Manufacturers handle that in one of two ways.

Rectified tile is mechanically ground on all four edges after firing, so every piece comes out dimensionally identical with a sharp, squared-off edge. Because the pieces are consistent, they can be set with very tight grout joints — often 1/16" to 1/8" — producing that near-seamless, monolithic look you see in contemporary spaces and large-format installations.

Non-rectified tile (also called pressed edge or cushioned edge) leaves the kiln as it is, with slight variation in size and a softly rounded edge. It needs a wider grout joint — generally 3/16" or more — to absorb that variance.

The trade-off is not about quality. It's about look and installation tolerance:

• Rectified gives you the minimal, seamless aesthetic — but it's unforgiving. With joints that tight there's nowhere to hide lippage, so the substrate has to be genuinely flat and the installer has to be good. Budget for floor prep.
• Non-rectified is more forgiving to install, and that soft pressed edge is exactly right for handmade, zellige, and traditional looks where a crisp machined edge would feel wrong.

A wavy, irregular zellige-look tile with a pressed edge isn't a lower-grade product. It's doing precisely what it's designed to do.

Glazed vs. Unglazed, and What's Underneath

A glaze is a liquid glass coating applied to the tile surface and fired on. It creates the color, the pattern, and the finish, and it seals the face of the tile.

Glazed tile is stain-resistant, never needs sealing, and can be made to look like virtually anything — marble, wood, concrete, hand-painted cement. The catch is that the design lives on the surface, so a deep chip can reveal a differently colored body underneath.

Unglazed tile — terracotta, quarry tile, certain technical porcelains — carries its color all the way through the body. Chips barely show. But the surface is more porous and usually wants a penetrating sealer to resist staining.

Between those two extremes, you'll see a few terms worth knowing:

• Through-body / full-body porcelain — color and pattern run entirely through the tile. Exceptionally durable; common in commercial specs.
• Color-body porcelain — the body is tinted to approximate the glaze color, so chips and cut edges are far less noticeable. This is the sensible middle ground and it's what you'll find in most quality residential porcelain.
• Double-loaded / double-charged — two layers of pigmented material pressed together, creating a thick wear layer.

PEI Rating: How Much Traffic The Tile Can Take

The PEI rating, developed by the Porcelain Enamel Institute and tested under ASTM C1027, measures how well a glazed surface resists abrasion from foot traffic and grit. A machine spins abrasive material across the glaze and records how many cycles pass before visible wear appears.

Class	Where it belongs
PEI 0	Walls only
PEI 1	Walls, plus very light-traffic barefoot areas such as a residential bath
PEI 2	Light residential floors — bedrooms, bathrooms
PEI 3	All normal residential floors — kitchens, hallways, living areas
PEI 4	Heavy residential and light commercial
PEI 5	Heavy commercial traffic

Two caveats that rarely get mentioned, and both matter:

First, PEI applies only to glazed tile. Unglazed and through-body products are evaluated with a deep abrasion test measuring volume loss instead — the absence of a PEI number on a full-body porcelain isn't a red flag.

Second, PEI is not a quality score. It describes glaze wear resistance and nothing else — not strength, not water absorption, not slip resistance. A PEI 1 wall tile can be a superbly made, expensive, gorgeous product. It simply isn't meant for a hallway floor. Don't let a low PEI talk you out of a wall tile.

DCOF: TL;DR - So You Don't Fall

DCOF stands for Dynamic Coefficient of Friction — a measure of how much grip a surface provides while you are in motion, as opposed to standing still. It's measured under the ANSI A326.3 standard using a tribometer on a surface wetted with a sodium lauryl sulfate solution, which simulates the thin film present when a slip actually happens.

The number to remember: a wet DCOF of 0.42 or greater is the generally accepted minimum for level interior floors expected to be walked on when wet.

The 2021 revision of the standard added five product use classifications, so manufacturers can be more specific than a single pass/fail:

• ID — Interior, Dry
• IW — Interior, Wet (kitchens, baths, entry foyers)
• IW+ — Interior, Wet Plus (showers, pool surrounds)
• EW — Exterior, Wet
• O/G — Oils and Greases

One important piece of honesty here, because it comes straight from the standard itself: DCOF testing "does not predict the likelihood a person will or will not slip." It's a tool for comparing surfaces under controlled conditions, not a safety guarantee. Real-world slip risk also depends on texture, tile size, grout joint frequency, footwear, and how well the floor is maintained.

Practical guidance: for a shower floor, smaller mosaic tile is often the smarter specification regardless of the DCOF number, simply because more grout joints mean more grip underfoot.

Shade Variation (V1 to V4): The Good And The Better

Every tile carries a variation rating describing how much color and pattern difference to expect from piece to piece.

• V1 — Uniform. Minimal difference between pieces.
• V2 — Slight. Subtle, consistent variation within one color family.
• V3 — Moderate. Noticeable differences. A single tile won't represent the whole floor.
• V4 — Substantial / Random. Dramatic variation. Two tiles from the same box may look like different products entirely.

This rating is behind almost every "the tile doesn't look like the sample" conversation in the industry. Highly varied tile — handmade looks, zellige, reclaimed and artisan styles — is designedto vary. That variation is the point, and it's what makes the finished installation look alive rather than printed.

But it means you should order samples, look at several pieces rather than one, and ask your installer to dry-lay the floor and pull from multiple boxes as they go, rather than working straight through one box at a time.

Related: tile is produced in batches, and both shade and caliber (the precise size) can shift slightly between production runs. Order your entire quantity, including overage, in one purchase.

Nominal vs. Actual Size (Yep, Every Tile Has Two Sizes...)

A "12x24" tile is rarely exactly 12" by 24". Nominal size is the rounded name; actual size is what you'd measure with a tape. A 3x6 subway tile is often closer to 2 7/8" by 5 7/8".

This is fine for general planning, but it matters when you're calculating a layout that has to land on a specific line, planning a pattern, or ordering coordinating trim. The actual dimensions are on the spec sheet — check them before you commit to a layout.

Additional Definitions:

• Bullnose / trim — a finished, rounded edge piece used to cap an exposed tile edge cleanly.
• Lippage — height difference between two adjacent tiles. Controlled by flat substrate prep and leveling clips.
• Substrate — whatever the tile is being set on: concrete slab, cement backer board, mortar bed.
• Thinset / mortar — the adhesive layer. Large-format tile requires a large-and-heavy-tile (LHT) mortar, not standard thinset.
• Sanded vs. unsanded grout — sanded for joints 1/8" and wider; unsanded for tighter joints and delicate polished surfaces that sand could scratch.
• Overage / waste factor — order 10% extra for a straight layout, 15% or more for diagonal, herringbone, or high-variation tile. It also leaves you spares for a future repair, which you'll be grateful for.
• Coverage / SF per box — tile sells by the box, not the piece. Always round up to full boxes when you calculate.
• Frost-proof — able to survive freeze/thaw cycling. Requires 0.5% or lower absorption plus manufacturer confirmation for exterior use.
• Finishes — polished (high shine), matte, satin, honed (smooth, low sheen), textured or structured (added grip), and lappato (semi-polished, part gloss and part matte).

Ok, So You've Read Everything. Now What?

You don't need to memorize any of it. When you're evaluating a tile, run through six questions:

1. Does the water absorption match the environment? Wet, exterior, or freeze/thaw means porcelain.
2. Does the PEI match the traffic? Glazed floors only — PEI 3 covers most homes.
3. Is there a wet DCOF figure? Check it for anything that will get wet, and consider texture and tile size alongside it.
4. What's the variation rating? Know it before you fall in love with a single sample.
5. Rectified or pressed edge? This sets your grout joint width and your floor prep budget.
6. Is it all coming from one batch? Order everything, plus overage, at once.

Answer those six and you've eliminated the overwhelming majority of tile buying regrets.

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Still deciding? Order samples and see the variation, edge profile, and finish in your own light before you commit — it's the single best thing you can do for a tile project. Browse the full collection or get in touch and we'll help you spec the right tile for your space.