Washfastness, also commonly known as colorfastness, is the term used to describe how well or poorly ink or dye bonds to a garment after multiple washes in a home or commercial washer. This is a top factor to be aware of when creating products for customers.
But, as always, there is no “blanket rule” to ensure good washfastness due to the wide variety of garments and ink options available.
Be sure to read the tech sheets from your ink manufacturer to ensure you are using the correct ink for the garment you’ll be printing. Follow manufacturer's guidelines for proper curing. Some inks may require additional additives to ensure adequate bonding and curing to substrates. If you can take a sample shirt home and run it through a couple of cycles in your home washer without fading, you can sleep easy.
There’s nothing more stressful than receiving a call that a customer's ink washed out of a shirt. It's costly to replace, and the stress of wondering if you are going to get more phone calls with the same issue might cost you some added sleep loss.
Source: Aaron Harris