Complex sentence: The key feature of dye-sublimated clothing is that the design is not printed on top of the garment, but permanently dyed into the threads of the shirt, ensuring that it will never fade.
Split into simpler sentences: The key feature of dye sublimated clothing is that the design is not printed on top of the garment. Rather, the design is permanently dyed into the threads of the shirt itself, ensuring that it will never fade.