In UV printing, choosing between hard ink and soft ink is critical for the durability of your product. Using the wrong ink can lead to cracking on flexible items or peeling on rigid ones. The difference lies in the elongation properties of the UV ink after it has been cured by UV light.

Hard UV Ink: Best for Rigid Substrates

Hard ink is formulated to create a tough, scratch-resistant surface. Once cured, it becomes very brittle and has almost no flexibility. It is designed to bond deeply with solid materials.

• Best For: Glass, metal, ceramic tiles, hard plastics (like acrylic), and wood. 

• Key Advantage: Exceptional scratch resistance and chemical durability. It won't scuff easily when items are handled or cleaned. 

• The Risk: If you apply hard ink to a flexible material (like a leather bag), the ink will shatter and crack as soon as the material bends.

Soft UV Ink: Best for Flexible Substrates

Soft ink (also known as flexible ink) contains specialized polymers that allow the ink to stretch after curing. Many professional soft inks can achieve an elongation rate of 100% to 200% without losing their bond.

• Best For: Leather, TPU (soft phone cases), canvas, vinyl, and silicone.

• Key Advantage: It moves with the material. You can fold, twist, or stretch the substrate, and the ink will remain intact. 

• The Risk: Soft ink is generally "stickier" and less scratch-resistant than hard ink. If used on a rigid metal sign, it may feel slightly tacky or be easier to scrape off with a fingernail.

Which Ink Should You Choose?

Most industrial UV printers, such as the Roland LEF2-200, allow you to load different ink types depending on your primary business focus.

If your shop produces a mix of both rigid and flexible items, some manufacturers offer a "Neutral" or "Medium" ink. This provides a middle ground—enough flexibility for some bending, but enough hardness for decent scratch resistance on rigid plastics.