Pretreatment

Pretreatment is the polymer solution sprayed or rolled onto a garment before DTG printing so the white ink has a surface to grip instead of a fiber to sink into and disappear — skip it on raw cotton and straight white ink dries a flat, grayish white instead of a clean, opaque one. Applied by machine or hand-pump sprayer and then heat-pressed or run through a dryer to flash off the moisture before a single drop of ink hits the shirt, the fluid cures into a surface the white underbase can sit on top of rather than get absorbed into.

This step is exactly why a dark-shirt DTG order runs more than the same design on a white blank: pretreatment adds a machine cycle, a dry time, and a slightly different hand at the print site, usually a faint stiffness or sheen where the fluid was applied. Light and white garments frequently skip the step entirely when the design doesn't need a white ink layer, which keeps that print noticeably softer to the touch.

Pros dial that dose to the fabric — heavier for 100% cotton, lighter for poly-blend tees, since over-application stiffens the hand and under-application leaves the white patchy and dull. Getting that ratio right, garment by garment, is a big part of what separates a shop's dark-shirt DTG work from a mediocre one.

Buyers sometimes assume pretreatment is an upsell a shop is tacking onto the invoice. It isn't optional on a dark garment — skip it and the white ink prints grayish and uneven, so the added cost reflects a mechanical requirement of the process, not a markup.