Fibers sticking up through an image, also known as fibrillation, can ruin a print. This is worse with certain garments and brands of pretreatment (FIREBIRD pretreatments actually contain a component to force fibers to stick to the shirt) and it is helpful to have a way to work around it.
Use a Paint Brush to Force Down Fibers
This is possibly the easiest, least expensive, and most effective way of dealing with fibers. Many printers who already use a brush to even out pretreatment spray patterns may be entirely unfamiliar with fibrillation. For this method, use a clean paint brush from any hardware store to push down fibers while the pretreatment is still wet. A quick brushing in a single direction will likely prevent the worst fibrillation. This should be every printer’s first choice for dealing with fibers as it is easy to use without interrupting work flow and won’t cause print complications.
Turn Up the Pressure on Your Heat Press
The reason that some brands of pretreatment require heavy pressure on a heat press is to fully press down fibers. FIREBIRD pretreatments are less likely to require this, but raising the pressure may sometimes still be helpful. FBX-100 and its related pretreats generally require a low pressure, but this can be turned up slightly for tougher prints. However, higher pressures may cause other issues, including staining and crystallization.
Save a Shirt After it Begins to Print
You may occasionally notice fibrillation on your white underbase before the colored ink is printed. When this happens, you can actually still save the print. Fibers poking through will only be visible if they can break through the CMYK inks, meaning that the white ink can be fixed. Lay a piece of cover paper (preferably a Teflon or silicone sheet like you use on the press) over the print. Then take something flat and rigid, like a business card, and gently scrape the white ink in one direction. Be sure to only go in a single direction and keep the ink evenly placed. While this method risks spreading ink where it is not meant to go, with a bit of luck it may just save your shirt.
Spray Water on Sweatshirts
Sweatshirts are some of the most likely items to suffer from fibrillation. These garments have so much fabric that some is bound to poke through the print. In addition to the previously mentioned methods, there is a lesser known fix for this issue. Using a spray bottle, apply a small layer of water over the area where you are printing. Then, brush this in a single direction (just like you do for the pretreat itself) and press the sweatshirt dry. This does not require much water and you should only need to press for a few seconds to dry the shirt. The water will help the fibers stay stuck down even before pretreatment is applied. Be sure to brush the pretreatment as well and keep an eye on the pressure. After this, your sweatshirt should be ready to print.