What Are the Main Materials Used for Heat Transfer Stickers?

1. Substrate: The Fundamental Carrier of the Design
   The substrate is the “skeleton” of a heat transfer sticker. It supports the printed design and adhesive, and must remain stable during heating (no melting or deformation). Common types include:

PET Film (Polyethylene Terephthalate)
The most common substrate, featuring excellent heat resistance (withstanding 150 °C–200 °C), high mechanical strength, low stretch deformation, and high transparency, making it ideal for printing. PET film is typically 25 μm–50 μm thick. After corona treatment, its surface adhesion to printing inks improves. Its advantage lies in strong thermal stability—during heating, it does not stick to the design or adhesive—ensuring smooth transfer. It is the preferred substrate for garment and fabric heat transfer stickers.

OPP Film (Oriented Polypropylene)
Lower in cost than PET, with high transparency and good flexibility, but slightly weaker heat resistance (suitable for 120 °C–160 °C environments) and prone to shrinkage under prolonged heating. Commonly used in low-temperature transfer applications (e.g., paper packaging, plastic toys), but unsuitable for high-temperature textile pressing (e.g., cotton, linen).

Release Paper (Silicone-Coated Paper)
Some simple heat transfer stickers use release paper as the substrate. A silicone coating provides release properties, paired with a lightweight printing layer and adhesive. Advantages include low cost and easy degradation, but heat resistance is limited (usually ≤140 °C), making it suitable for disposable or short-term uses (e.g., holiday decorations, temporary labels).

2. Printing Layer: The Core of the Visual Design
   The printing layer is the “face” of the heat transfer sticker, which must transfer completely to the receiving surface during heating, with bright colors and abrasion resistance. Material choice is closely linked to printing technology:

Inks

Heat Transfer Ink: Specially formulated for thermal transfer, made of pigments, resins, and solvents. Under heat, it separates from the substrate and bonds to the receiving surface. Resins are usually polyester or polyamide types to ensure fluidity at high temperatures and firm adhesion to fabrics, plastics, etc.

Sublimation Ink: A special disperse dye ink that sublimates into gas under heat, penetrating and fixing within polyester fibers. Suitable for dark or tightly woven fabrics (e.g., sportswear, polyester T-shirts), offering breathability and good wash fastness.

Metallic Foil / Pigment Foil
Used for gold or silver stamping effects, typically made from aluminum foil (metal-coated) or polyester film (coated with metallic pigments). Metallic foil requires special hot-melt adhesives. When heated, the adhesive melts, transferring the foil design to the receiving surface, producing a bright metallic finish. Common in bags and gift packaging decoration.

3. Adhesive: The Key to Heat Transfer
   The adhesive acts as the “bridge” between the heat transfer sticker and the receiving surface. It must remain non-tacky at room temperature but activate under heat. Common types include:

Hot-Melt Adhesive
The most common adhesive for heat transfer stickers, typically made from EVA (ethylene-vinyl acetate copolymer), tackifiers, and waxes. Solid at room temperature, it melts at 80 °C–160 °C to become tacky, then quickly solidifies upon cooling to form a strong bond. Formulations vary based on substrate:

For fabrics (cotton, polyester): Use low-melting-point EVA (80 °C–120 °C) to prevent fiber damage and ensure strong wash resistance.

For plastics (PP, PVC): Use high-viscosity formulas to improve adhesion to non-polar surfaces.

For paper: Use low-tack adhesives to prevent wrinkling or tearing.

Thermosetting Adhesive
Made from epoxy resin, polyurethane, etc., these undergo a chemical curing reaction when heated, forming an irreversible and tough adhesive layer. Ideal for extreme weather resistance (e.g., outdoor goods, industrial labels). Requires higher curing temperatures (≥180 °C) and costs more, thus used only for special needs.

Modified Pressure-Sensitive Adhesive
Used in some low-temperature heat transfer stickers, where heating (60 °C–100 °C) boosts tackiness for transfer. Advantage: low operating temperature—suitable for heat-sensitive substrates like leather or foam—but with weaker water and durability performance.

4. Release Layer: Ensuring Complete Design Transfer
   The release layer lies between the substrate and printing layer, reducing adhesion so the design can cleanly detach from the substrate and transfer during heating. Common materials include:

Silicone Coating
The most common release material. Silicone (polydimethylsiloxane) is coated on PET or OPP films, creating a low surface energy release layer. Release force can be adjusted: high release for complex designs (to prevent tearing during transfer), low release for simple designs (easier peeling).

Fluorine-Based Release Agent
Superior to silicone in performance, with higher heat resistance (withstanding over 200 °C) and more stable release force. Suitable for multiple pressings or high-temperature processes (e.g., industrial part marking). Higher cost limits its use to premium heat transfer stickers.

5. Functional Auxiliary Layers: Enhancing Durability and Adaptability
   Some heat transfer stickers feature additional layers to boost specific properties:

Abrasion-Resistant Coating
Applied over the printing layer, made from polyurethane or acrylic resin, to improve scratch and wash resistance (e.g., children’s clothing stickers that withstand repeated washing).