Nearly every tile sold as “tile” is one of two things: ceramic or porcelain. They are the same family of product, made from the same basic ingredients, and the difference between them comes down to how they are manufactured and one measurable number. This page explains what that difference actually is, how to read the ratings on a spec sheet, and where each one belongs in a house. If you already know what you want, our ceramic tile and porcelain tile pages cover each in more detail, and natural stone is a different category entirely.
How ceramic tile is made
Ceramic tile is made of clay that is shaped and fired in a kiln. After the clay and minerals are refined they are ready to be shaped, and the most common method is the dust press: an almost dry mixture of clays, talc and other ingredients is pressed into a mold at extremely high pressure. The newly formed tiles are then fired to harden the material.
After firing, tile is finished one of two ways.
Unglazed. The pigment or natural color is present during firing and is part of the tile body itself. Because the color runs through the tile, a chip does not expose a different color underneath. Unglazed tile generally needs to be sealed for stain resistance.
Glazed. Color is added after firing as a glasslike surface bonded to the tile. Glazing allows brighter colors and a far wider range of looks than unglazed, and it adds stain resistance without sealing. The tradeoff is that the color is a surface layer – deep damage shows the body color beneath.
Ceramic is the most versatile tile surface precisely because the glaze is man-made. It is available in an almost infinite range of colors, patterns and styles, and it suits nearly every interior application.
What actually makes a tile “porcelain”
Porcelain tile is a ceramic tile, made by the same dust-pressed method, from a composition that fires denser. The result is a tile that is fine grained, smooth, and sharply formed. But “porcelain” is not a marketing word – it has a definition with a number attached.
Under ANSI A137.1, the American National Standard for ceramic tile, porcelain is tile with a water absorption of 0.5% or less, measured per ASTM C373. That puts it in the impervious category, the least absorptive class there is. Everything else is some grade of ceramic. That single number is the whole distinction, and it is why porcelain is the right call in wet areas: a body that will not take on water will not carry moisture into places it should not go.
It is worth saying plainly that impervious tile is not the same thing as a waterproof installation. Water does not go through porcelain, but it will happily travel through grout joints and around the tile if what is behind it was never waterproofed. That is a substrate question, not a tile question, and it is where most shower failures actually start – see why tile installations fail and our Schluter Kerdi shower preparation page.
Reading the ratings
Three numbers appear on most spec sheets, and two of them are widely misread.
Water absorption is the one that matters most and the one described above. Under 0.5% is porcelain and impervious. Higher figures are still perfectly good tile, they just belong in drier places.
PEI rates glaze wear – how well the glazed surface resists abrasion – on a scale of I through V. It is a surface rating, not a strength rating, and it says nothing about the tile body. Unglazed porcelain carries no PEI rating at all, which regularly confuses people into thinking it is unrated or inferior. For most residential floors a PEI III or IV glazed tile is plenty.
DCOF is the slip-resistance measurement, tested under ANSI A326.3. The threshold is a wet DCOF of 0.42 or greater for level interior floors expected to be walked on when wet. Two caveats come from the standard itself and are worth repeating: DCOF is not a guarantee that a slip cannot happen, and hitting 0.42 does not automatically make a tile appropriate for every location. A polished tile that meets the number on a test machine can still be a poor choice for a shower floor, which is one reason small mosaics with a lot of grout joint are a common shower-floor answer.
Rectified edges and large format
Tile comes out of the kiln with slight size variation. Rectified tile has been mechanically ground after firing so every piece is the same dimension with a crisp square edge, which is what allows the very tight grout joints people usually have in mind when they picture a modern floor. Non-rectified tile needs a wider joint to absorb the variation – not a defect, just a different look and a lower price.
Large-format tile is spectacular and unforgiving. The bigger the tile, the flatter the substrate has to be, because a floor that is out of plane shows up as lippage at every single edge. Long uninterrupted runs also need movement joints. This is the single most common place we see a well-chosen tile installed badly – the tile was never the problem. Our installation methods page covers how we prepare for it.
What this means in a Colorado house
Two local realities change the answer here. Front Range soils are expansive and our seasonal swings are large, so floors move more than people expect; an installation that does not accommodate that movement is where cracks come from. And anything outdoors – patios, outdoor kitchens, exposed steps – goes through repeated freeze-thaw cycles. That is a straightforward case for impervious porcelain, because an absorptive tile that takes on water and then freezes will eventually break itself apart.
Choosing for the room
Once you know the categories, the decision is mostly about location:
- Floor tile – through-body or well-glazed porcelain for high-traffic areas, entries and mudrooms
- Shower tile – porcelain or glazed ceramic on walls, with slip resistance driving the floor choice
- Bathroom tile – the whole room, where moisture and cleanability lead
- Kitchen tile and backsplashes – where looks can lead, since the wear demands are low
- Glass tile and mosaics – accents, niches and shower floors
- Natural stone – a different material with different rules, including sealing
Grout matters as much as the tile in wet and high-traffic areas; how to pick the perfect grout covers epoxy versus cementitious. And if you are still deciding room by room, how to choose the correct tile walks through it.
Talk it through with someone who installs it
Spec sheets only get you so far. We are a Certified Tile Installer (CTI #847) based in Fort Collins, installing tile since 1998, and we will tell you when a tile you like is wrong for the room before it gets ordered. Call (970) 213-3682 or use our contact form. See finished work in the gallery, or read common questions on our FAQ page.