If you’ve ever used a T shirt press (or any heat press) for sublimation, you’ve probably noticed a frustrating pattern: the same design can look bright and crisp on a polyester tee, but end up dull, faded, or short-lived on 100% cotton. It’s easy to blame your printer settings or time and temperature, but the real reason is more fundamental than that.

Sublimation isn’t “ink sitting on top of fabric.” It’s a dye process that depends on how certain fibers behave under heat. Once you understand what the dye is trying to do at a molecular level, the polyester requirement stops feeling like a picky rule and starts looking like simple materials science.

Most sublimation inks rely on disperse dyes. During pressing, several steps happen in sequence:

You print the design onto sublimation paper, place it on the shirt, and apply heat. At sublimation temperatures, the dye transitions from a solid to a gas. That phase change is the “sublimation” in sublimation printing.

When you close the T shirt press, the combination of heat and pressure forces the dye vapor into close contact with the fabric surface. If the fiber is compatible, the dye can migrate into the fiber structure instead of lingering on the surface.

As the shirt cools, the dye becomes trapped inside the fiber. That’s why a good sublimation print has no heavy film feel—the color is effectively embedded rather than layered.

Practical result: on the right fabric, sublimation produces smooth hand feel, strong wash durability, and sharp detail.

Polyester is a thermoplastic polymer fiber. Under the heat levels used in a heat press, polyester becomes more receptive at a microscopic level—making it easier for disperse dye vapor to diffuse into the fiber.

• Disperse dyes have high affinity for polyester
• The dye vapor can penetrate and bond within polyester fibers
• Once cooled, the dye is physically locked in, which supports long-lasting color

This is also why higher polyester content usually means:

• brighter color
• cleaner edges
• more consistent results across different production runs

If you want the classic sublimation look—vibrant and embedded—100% polyester is the most reliable choice.

Cotton is primarily cellulose, not a plastic-like polymer. Disperse dyes are not designed to bond well with cellulose, so even if your heat press settings are perfect, the chemistry still isn’t on your side.

The dye vapor may transfer partially, but it typically:

• struggles to migrate into cotton fibers in a stable way
• stays closer to the surface
• washes out or fades much faster than on polyester

• colors look muted or “vintage”
• small text and thin lines lose punch
• wash durability is noticeably weaker

So cotton isn’t “bad”—it’s simply not compatible with the way sublimation dye is meant to lock in.

When someone says they sublimated successfully on cotton, they’re usually using a workaround that adds a receptive layer for the dye.

A coating creates a surface that behaves more like a polymer layer that disperse dyes can penetrate.

• Pros: can improve brightness on cotton
• Cons: can feel stiff or plasticky, may apply unevenly, durability varies

You sublimate onto the HTV layer (or through it, depending on the product), then bond that layer to cotton using a T shirt press.

• Pros: makes cotton projects possible with more predictable color
• Cons: introduces a “layer” feel and changes breathability compared to true fiber-dye bonding

In both cases, you’re not changing cotton’s chemistry—you’re adding a compatible surface.

Here’s a simple way to select materials and set expectations:

• Best true sublimation results:
  White or light 100% polyester tees + consistent pressure/time/temp + quality sublimation paper

• Comfort + acceptable sublimation:
  Poly blends (like 65/35 or 50/50). Expect slightly softer, more muted color.

• 100% cotton:
  Avoid direct sublimation if you need bright color and long wash life. Use coating or sublimation HTV if cotton is non-negotiable, and plan for the feel/durability trade-offs.

A heat press or T shirt press can’t force incompatible chemistry to behave. Sublimation works when dye vapor can move into—and stay inside—the fiber. Polyester welcomes disperse dye and locks it in. Cotton doesn’t, so the print tends to sit closer to the surface and fade faster. Once you know that, choosing blanks (and choosing the right method for cotton) becomes straightforward and repeatable.