How much curl is acceptable in modular carpet and vinyl flooring products

Author Note

The body of this article was written by Sim Crisler, an associate of LGM and an expert in carpet tile and vinyl flooring materials. Sim is a chemist and spent 33 years with Milliken Carpet. We have added updated information to this issue and included vinyl flooring as well.

Modular Carpet: Engineering from the Ground Up

Essentially every manufacturer in the commercial flooring market offers at least one modular carpet product—also known as carpet tile. Each has learned, sometimes painfully, that modular carpet is not simply broadloom carpet cut into pieces. To be successful, it must be engineered from the floor up as a modular product.

Planar stability, or flatness, has always been a significant issue for modular carpet manufacturers. By definition, modular carpet is shipped and installed in small pieces. Each piece must perform as a unit and be engineered to be:

Flat
Square
Stable
Equal to or exceeding the performance criteria of roll-form carpet

Since each module has four cut edges that butt against adjacent modules—without seam sealing or edge protection as in broadloom—it is imperative that:

Tuft bind strength is excellent
Modules are cut perfectly square

Failure to meet these standards leads to fuzzy, frayed edges and visible gaps between tiles.

Common Issues

Carpet Tile—Edge Lift
Carpet Tile—Not Cut Square

These issues are often visible and can compromise both aesthetics and safety.

Curl and Cup: Definitions and Causes

A lack of planar stability may manifest as:

Curl: Edges and corners lifting off the substrate
Cup: Areas away from the edges lifting

These are potential job site failures and safety hazards.

Root causes typically include differential tension levels within the product. Modular carpets are complex, multilayered constructions:

Top Layer: Usually tufted carpet
Primary Backing: Critical for planar stability; must resist elongation or compression during manufacturing
Binder Layer: Secures tufts and imparts face properties
Backing Material: Often thermoplastic, applied below the binder
Stabilization Element: Typically a non-woven Fiberglas fleece
Final Backing Layer: Embossed for floor contact
Optional Cushion Layer: Sometimes polyurethane with a felt or fleece outer layer
Outer Layer Composition: Felt or fleece made up of a combination of different fibers depending on the properties desired

Regardless of the configuration, this is a complex multilayered product. Any differential tension between these layers can result in a finished product that is inherently curled or cupped. This issue is not limited to carpet tile—it can also affect vinyl tile and plank.

Backing Composition and Recycled Content Risks

Another potential source of planar stability issues is the composition of the backing material. This applies to both PVC and other lower melting olefinic thermoplastics, which dominate the market today.

These materials are often chosen for their ability to incorporate recycled content, whether from postindustrial or post-consumer sources. The process is relatively simple: reclaimed material is re-melted and introduced into the production stream alongside virgin material.

However, if the recycled content introduces elements that expand and contract in response to normal environmental variations, the product becomes a ticking time bomb. Curling will occur regardless of how well the substrate is prepared or the installation is executed.

The Adhesive Myth

Some manufacturers seem to believe that producing modular carpet with an inherent tendency to curl or cup is acceptable—as long as they engineer an adhesive strong enough to hold it down. Their operating assumption:

“Don’t worry about the curl. We’ve got our ‘Snot on a Screen Door Super Dooper 1000’ adhesive. We’re going to glue these bad boys down so tight that they won’t even be able to think about curling.”

To quote a well-known college football coach:

“Not So Fast My Friend.”

This assumption is fundamentally flawed. If a modular carpet or vinyl flooring product has an inherent tendency to curl, it will eventually curl—no matter the type or amount of adhesive used. Even the most aggressive adhesives (epoxies, polyurethanes, contact cements) may suppress curl temporarily, but it inevitably reappears.

What remains is a compromised installation that requires modules to be cut into one-inch strips just to remove them from the floor.

Adhesives: Purpose and Limitations

Adhesives in modular carpet installations are intended only to prevent lateral movement. They should not require excessive force to remove modules, nor should they damage the product during removal.

Customers who pay a premium for modular carpet deserve a product that meets the serviceability and flexibility they were promised. They did not purchase broadloom with seams every 18″, 24″, or 36″.

While aggressive adhesives do resist lateral movement, they often make it difficult to use the carpet as a modular system. And they do not solve long-term planar stability issues.

Industry Perspective and Final Analysis

Sim Crisler shares his personal experience:

“I’ve been closely involved in the development, manufacture, and installation of modular carpet since it entered the U.S. market in the early 1970s. I’ve seen hundreds of millions of yards of properly engineered modular carpet perform flawlessly. That we even ask ‘How much curl is acceptable?’ defies logic. It’s like asking how much rat excrement is acceptable in baby food.”

The answer is simple: Zero.
Modular carpet should lie flat, square, and stable straight out of the box—and remain that way throughout its lifespan.

This same standard applies to vinyl tile and plank or any multilayered PVC or PVC-free flooring product. These products must be:

Flat
Square
Stable
Free of dimensional or planar changes

Balanced product layers are essential. Any imbalance—including in the polyurethane wear layer—can cause distortion. Adhesives cannot prevent these changes; internal stress will overpower adhesion.

Acclimation and Environmental Realities

Acclimation is not always the root cause of issues with LVT or LVP. Vinyl naturally expands with heat and contracts with cold. Saying you don’t need to acclimate the product before installation—but must acclimate the space afterward—is nonsensical.

The product will seek equilibrium and react. And the installer pays the price.

Final Thoughts

Modular flooring—whether carpet tile, vinyl tile, or plank—must be flat, square, and stable out of the box. Installation cannot change this.

Industry publications confirm ongoing stability problems. The rise of new product variants only adds uncertainty.

Instability in carpet tile, vinyl plank, rubber tiles, and hybrid materials is one of the biggest challenges in flooring today. That’s why it’s critical to:

Know your products
Source from manufacturers who control their processes
Seek expert help when problems arise