Polyester fabrics are more sensitive to heat than cotton fabrics. Cotton products tend to shrink after being washed and dried, where polyester products are prone to shrink when initially subjected to heat. To properly screen print on polyester it is important to control and manage your heat during the curing process. Too much heat can damage a garment in several ways including excessive shrinkage, dye migration, and scorching. You may need to use printing inks that have been formulated to cure at lower temperatures. Exposing polyester products to high temperature risks the quality issues mentioned above. You should monitor the surface temperature of the garments being cured with a thermoprobe, temperature tapes, and/or a pyrometer. Please also follow the print parameters set by the ink manufacturer.
Temperatures needed to cure screen printing inks or apply heat transfers may also convert some of the dyes in the polyester into a gas. If this occurs, the polyester dyes could permeate into the ink or transfer and change its original shade. To avoid this, it is highly recommended to use inks or transfers that are bleed resistant. Dye migration can be apparent almost instantly or could take several hours or even several days to manifest. It’s particularly advisable to wait at least 24 hours before shipping a finished product if you are unfamiliar with the garment, inks or transfers.