Subway tiles are often associated with clean lines, classic proportions, and durable everyday surfaces, but their performance depends heavily on the material they are made from. Porosity—the degree to which a tile can absorb moisture, oils, or other liquids—plays a major role in where subway tiles can be used, how easily they clean, and how well they hold up over time.

In kitchens, bathrooms, showers, and other moisture-prone spaces, understanding porosity helps determine whether a tile is suitable for the application or whether it needs additional protection, such as sealing. A glazed ceramic subway tile, for example, behaves very differently from an unglazed ceramic tile or natural stone option. This guide explains what porosity means, how it affects subway tile performance, and which materials are best suited for different interior and exterior uses.

 

Mikayla 2.5x5 Glossy Ceramic Tile in Eggshell creates a soft shower backdrop, complemented by brass fixtures, a glass enclosure, dark drapery, and a freestanding tub with a lake-facing view.

 

Understanding Porosity

Porosity refers to the amount of empty space within a material’s structure. These microscopic openings, often called pores or voids, can influence how easily water, oil, vapor, and cleaning solutions interact with the tile. In practical terms, the more porous a tile is, the more likely it is to absorb liquids into its surface or body.

Porosity and Its Effects on Tiles

The porosity of a subway tile directly affects how it performs in real-life conditions. In dry decorative areas, a slightly more porous material may not create major concerns. In kitchens, bathrooms, showers, laundry rooms, or outdoor spaces, however, absorption becomes much more important.

 

Liquid Absorption

Porous tiles can absorb water, oils, soaps, and other liquids. Once moisture enters the tile body, it may leave behind stains, mineral deposits, or residue as it evaporates. In some cases, absorbed moisture can contribute to efflorescence, a white chalky deposit caused by salts moving to the surface. Repeated water exposure may also weaken certain materials over time, especially if the tile is not sealed or properly installed.

 

Staining Resistance

Low-porosity subway tiles are generally easier to maintain because liquids remain on the surface rather than soaking into the material. This gives homeowners more time to wipe away spills before they become stains. Glazed ceramic and porcelain subway tiles are commonly favored for backsplashes and bathroom walls for this reason, as their dense or coated surfaces help resist everyday splashes, cooking residue, and cleaning moisture.

 

Freeze-Thaw Durability

Porosity becomes especially important in outdoor or unconditioned spaces. If water enters a porous tile and then freezes, it expands inside the material. That expansion can create internal pressure, leading to cracking, spalling, or surface damage. For exterior installations or areas exposed to freezing temperatures, dense, low-absorption materials such as porcelain are typically more reliable than highly porous ceramic, terracotta, or natural stone.

 

Chemical Sensitivity

Porosity can also affect how a tile responds to cleaning products. More absorbent materials may allow acidic, alkaline, or harsh chemical cleaners to penetrate the surface, which can lead to dulling, etching, discoloration, or gradual material breakdown. Natural stone is especially sensitive to cleaner selection, while glazed ceramic and porcelain are typically more resistant when maintained with appropriate non-abrasive products.

 

Types of Porosity

Porosity is not only about how many pores a material contains, but also how those pores are arranged. The structure of the pores determines whether liquids remain near the surface or move deeper into the tile body.

 

Open Porosity

Open porosity occurs when pores connect to one another and create pathways through the material. This makes it easier for water, oils, and other substances to penetrate the tile. Open porosity is more concerning in subway tile applications because it increases the risk of staining, moisture retention, efflorescence, and long-term water damage. Unglazed ceramic, terracotta, and many natural stones can have higher open porosity, which is why they often require sealing when used in kitchens, bathrooms, or other moisture-prone areas.

 

Closed Porosity

Closed porosity refers to pores that are sealed off within the material rather than connected to the surface. Because these voids do not form continuous channels, they are less likely to absorb surface liquids. Dense porcelain tiles and well-glazed ceramic subway tiles typically perform well in this regard, especially when the finished face is intact. Even so, installation details still matter. Grout lines, cut edges, and unsealed backs can influence the overall moisture resistance of the finished surface.

Understanding the difference between open and closed porosity helps clarify why not all subway tiles perform the same way. Two tiles may look similar once installed, but their absorption rates, surface finishes, and material density can make one better suited for a shower wall, while another may be more appropriate for a dry decorative feature.

 

Aniston 3x12 Polished Porcelain Tile in Calacatta Top brings movement to the shower wall through a herringbone layout, balanced by matte black fixtures, a rounded mirror, and a clean white vanity.

 

Materials Used in Subway Tiles

When choosing subway tiles for your kitchen or bathroom, the material you select is just as important as the design. Different materials offer unique benefits, from durability and water resistance to aesthetic appeal. Here are the most common materials used in subway tiles to help you make an informed decision that meets both your practical needs and design aspirations.

Ceramic

The reigning champion of subway tiles, ceramic offers a classic look and affordability. Generally considered non-porous or low porosity (water absorption less than 0.5%). This makes them ideal for kitchens, bathrooms, and other moisture-prone areas. However, porosity can vary depending on the manufacturing process. Imperfections in the glaze or improper firing can result in higher porosity tiles, making them more susceptible to staining and requiring extra care. Most ceramic subway tiles come glazed, creating a smooth, non-porous surface. Unglazed tiles, while less common, offer a natural, earthy look but are more porous and require sealing for use in wet areas.

Porcelain

A step up from ceramic, porcelain is a denser, more refined ceramic tile with even lower porosity (typically less than 0.5% water absorption). This exceptional density translates to near imperviousness to moisture, making porcelain subway tiles a top choice for high-moisture environments like shower walls and backsplashes. Porcelain's superior strength also allows for larger format subway tiles, opening up design possibilities. 

Natural Stone

Natural stone subway tiles can elevate a space with their inherent beauty and variation. Popular options include marble, granite, slate, and travertine. Natural stone is porous but its porosity varies depending on the specific type. Marble, for example, is more porous than granite.

Sealing natural stone subway tiles is crucial to protect them from staining and water damage. The sealant needs to be periodically reapplied based on usage and the stone's properties.

Recycled Content and Tile Variations

For environmentally-conscious buyers, some subway tiles are made from recycled contents or materials like glass or porcelain, offering a sustainable option with a classic look—though checking their porosity is essential. Additionally, porosity can vary between different manufacturers or product lines, so it's important to review the technical specifications provided by the tile supplier.

 

 

Jaden 2.5x16 Glossy Ceramic Tile in Tender Gray forms a calm kitchen backsplash, framed by sage cabinetry, marble countertops, brass hardware, and a warm wood range hood.

 

Selecting Subway Tiles for Different Applications: Balancing Porosity and Performance

Understanding how porosity interacts with the intended use of the subway tiles is crucial for ensuring optimal performance and longevity. Let's delve deeper into how porosity affects suitability for different areas:

Backsplashes

This high-splash zone demands a material that can handle moisture without succumbing to stains or water damage. Here, non-porous options like porcelain subway tiles or glazed ceramic subway tiles reign supreme. Their low water absorption rate minimizes the risk of liquids penetrating the tile body and causing staining. Additionally, their smooth surfaces make them easy to clean, maintaining a pristine appearance. We have an innovative Augmented reality (AR) tool so you get to see how subway tiles will look as your backsplashes.

Shower Walls 

Similar to backsplashes, shower walls are constantly exposed to moisture. Porosity becomes a critical factor, as water infiltration behind the subway tiles can lead to mold growth and structural damage. For shower walls, non-porous ceramic or porcelain subway tiles are an excellent choice. Their near-impervious nature provides peace of mind, knowing moisture won't compromise the integrity of the wall system. 

Floors

While not the most traditional application, some porcelain subway tiles with a matte finish can be used for flooring, particularly in powder rooms or mudrooms. In this case, porosity becomes less of a concern compared to backsplashes or shower walls. However, a new factor emerges: slip resistance. Subway tiles, with their smooth surface, can be slippery when wet. Choose subway tiles with a textured or matte finish that provide better traction underfoot, especially in areas prone to moisture. It's important to note that some local building codes might have specific requirements for slip resistance in flooring materials. Mosaics with a matte or textured finish are also recommended for bathroom or shower flooring since they offer extra grip.

Outdoor Use

When considering subway tiles for patios, balconies, or other exterior applications, porosity becomes a major concern. Outdoor environments expose tiles to fluctuating temperatures, including freezing conditions. Water trapped within the pores of a porous tile can expand when it freezes, exerting immense pressure that can crack or damage the tile. Therefore, for outdoor use, prioritize non-porous materials like porcelain subway tiles. This material offers superior resistance to water infiltration and freeze-thaw damage, ensuring your subway tile installation endures the elements.

 

Astrid 3x6 Matte Porcelain Mosaic Tile in Sand adds subtle vertical rhythm to the shower wall, paired with brushed brass fixtures and warm light that highlights its soft stone-like variation.

 

Simple Tests to Assess Tile Porosity

Before committing to a subway tile installation, especially for natural stone or unglazed ceramic options, testing their porosity provides valuable insights. Here's a breakdown of a simple yet effective method:

The Water Drop Test

This quick and easy test offers a preliminary indication of a subway tile's porosity. Here's how to conduct it:

Gather your materials

You'll need a clean, dry tile sample and a dropper or eye dropper.

Locate an uncoated surface

For glazed subway tiles, the glazed side is generally non-porous. Focus on the uncoated back or edge of the tile for the test.

Apply a drop of water

Using the dropper, place a small drop of water (around the size of a pea) on the uncoated surface of the subway tile.

Observe the water behavior

If the water beads up and forms a tight droplet on the surface, congratulations! The subway tile is likely non-porous or has very low porosity. This indicates good resistance to staining and moisture absorption. If the water is absorbed readily by the tile and spreads out, the subway tile is likely more porous. Sealing the subway tiles before installation, especially in areas prone to moisture, is highly recommended to minimize staining and water damage.

Limitations of the Water Drop Test

While the water drop test is a handy initial assessment tool, it has limitations. Here's what to keep in mind:

Accuracy

The test provides a basic idea but may not reveal the exact porosity level. A more precise measurement can be done using specialized equipment in a laboratory setting.

Variations within a batch

Even within the same batch of subway tiles, there might be slight variations in porosity. Testing multiple tiles is recommended for a more comprehensive understanding.

Alternative Methods

For a more precise measurement of porosity, professional subway tile stores or contractors might have access to porosity meters. These electronic devices measure the water absorption rate of a tile sample, providing a more accurate percentage of porosity.

Edward Martin offers premium porcelain and ceramic subway tiles that are non-porous, which means they are resistant to heat, moisture, and scratches. We also have experienced professionals who are not only dedicated to bringing your dream design to life but will also give advice on which subway tiles are perfect for your shower or bathrooms.

 

Chantel 3x12 Matte Porcelain Tile in Imperial gives the backsplash a layered gray marble look, complemented by natural wood cabinetry, stone vessels, and understated countertop styling.

 

A Guide to Keeping Your Subway Tiles Sparkling

The timeless beauty of subway tiles is undeniable, but maintaining their pristine look requires proper cleaning and care routines. Here's a breakdown of essential maintenance practices for different subway tile materials:

Non-Porous Tiles (Glazed Ceramic and Porcelain)

The good news is that non-porous glazed ceramic and porcelain subway tiles are generally low-maintenance. Their smooth, non-absorbent surfaces make them easy to clean and resistant to staining. Here's what you'll need:

Routine Cleaning

For regular cleaning, a mild detergent diluted with warm water and a soft, non-abrasive cloth (like microfiber) is sufficient. Wipe down the tile surface to remove dust, grime, and everyday splashes.

Deeper Cleaning

For occasional deeper cleaning, you can use a store-bought tile cleaner specifically formulated for ceramic or porcelain subway tiles. Always follow the manufacturer's instructions for dilution and application.

Avoid Harsh Chemicals

Avoid using abrasive cleaners, scouring pads, or harsh chemicals, as they can scratch the glazed surface and dull the shine over time.

Porous Tiles and Natural Stone

For porous tiles like unglazed ceramic or natural stone subway tiles, a slightly different approach is necessary:

Specialized Cleaners

Opt for a pH-neutral cleaner specifically designed for the type of natural stone you have (e.g., granite cleaner, marble cleaner). Harsh acidic or alkaline cleaners can damage the stone's surface.

Sealing

Natural stone is inherently more porous and prone to staining. Sealing the tiles with a penetrating sealer helps create a barrier against moisture and stains. Sealing should be done before installation and periodically resealed based on usage and the specific sealant's recommendations. Consult a stone care professional for guidance on the appropriate sealer and application process.

Stain Removal

Address spills promptly to prevent them from setting in. Blot up any spills with a clean, absorbent cloth. For tougher stains, consult a stone care specialist for recommendations on safe and effective cleaning methods.

 

Shea 3x12 Matte Porcelain Tile in Dune creates a quiet horizontal backdrop behind the cooktop, balanced by gray stone counters, wood cabinetry, and a simple tray of fruit.

 

Grout: The Vital Partner in Subway Tile Installations

While subway tiles take center stage, grout, the unsung hero, plays a critical role in the overall functionality and aesthetics of your tiled surface. Grout fills the gaps between tiles, ensuring stability and a uniform appearance. However, it's important to remember that grout can be more porous than the tiles themselves. This porosity can lead to several potential drawbacks:

Staining

Grout's porous nature makes it susceptible to absorbing stains from dirt, mildew, and colored liquids. This can lead to unsightly discoloration and detract from the overall beauty of your installation.

Mold Growth

In damp environments, unsealed grout can become a breeding ground for mold and mildew growth. The dark, damp environment within the pores provides ideal conditions for these organisms to thrive, posing potential health concerns and creating unsightly black marks.

Cracking

Over time, unsealed grout can become brittle and prone to cracking, especially with exposure to moisture and temperature fluctuations. This can compromise the structural integrity of the subway tile installation and create an entry point for water infiltration behind the tiles.

The Power of Sealing Grout

Sealing your grout after installation is a simple yet crucial step to prevent these issues. Here's how sealing benefits your subway tile installation:

Stain Resistance

A penetrating sealer creates a barrier on the grout's surface, reducing its ability to absorb stains. Spills and dirt will bead up on the surface, making them easier to clean and minimizing the risk of permanent discoloration.

Mold Prevention

By sealing the grout, you eliminate the moist environment in which mold thrives. This helps prevent the growth of mold and mildew, promoting a healthier and more hygienic environment.

Enhanced Durability

Sealers strengthen the grout, making it more resistant to cracking and wear and tear. This extends the lifespan of your grout and reduces the need for repairs or regrouting.

Choosing the Right Grout

Selecting the appropriate grout is crucial for your project. Sanded grout, which contains fine sand particles, is best for wider grout lines (1/8 inch or more) and provides structural support. Unsanded grout, which lacks sand particles, is ideal for narrower grout lines (less than 1/8 inch) and offers a smooth, finished appearance.

Ensuring Longevity with Proper Grout and Maintenance

Grout and maintenance play a significant role in the longevity and appearance of your subway tile installation.

Grout

While we've focused on the porosity of the tiles themselves, it's important to remember that grout, the material filling the gaps between tiles, can be more porous than the tiles. Sealing the grout after installation is crucial for preventing moisture penetration, mold growth, and staining, regardless of the chosen tile material.

Maintenance

Even with non-porous subway tiles, proper cleaning and maintenance are essential for long-lasting beauty. Regular cleaning with appropriate cleaning solutions helps prevent dirt and grime buildup and ensures a sparkling appearance. For porous materials like natural stone, additional maintenance steps like resealing might be necessary depending on the specific material and usage.

Porosity and Your Subway Tile Project

Subway tiles offer timeless design and versatility, but their success hinges on selecting the right material for the intended application. Understanding porosity, the enemy of moisture-prone areas is key. By considering the porosity of different subway tile materials and how they interact with factors like water exposure and freezing temperatures, you can make informed choices.

Opt for non-porous options like porcelain and ceramic subway tiles for backsplashes and shower walls. Embrace the beauty of natural stone with proper sealing for a touch of luxury. Remember, grout, though often overlooked, plays a vital role. Sealing it creates a barrier against staining, mold, and cracking. With this knowledge in hand, you can confidently select the perfect subway tile material, ensuring a beautiful and durable installation that graces your space for years to come.