Dyed into the material
Direct-to-fabric printing prints the cloth itself, on the roll, before a single piece is cut. The garment is then cut and sewn from that printed fabric, so colour runs continuously across panels and seams and the design is part of the material rather than a layer on it. It is the method behind continuous prints on natural fabrics — and despite the name it has nothing to do with DTF, which stands for Direct-to-Film and presses a transfer onto an item that has already been made.
A roll of blank cloth passes through a wide-format printer and comes out the other side as printed fabric. Only then is it laid out, cut into panels and sewn. The consequence is that there is no "print area" in the usual sense — the whole bolt carries your design, and whichever part of it a panel is cut from is what that panel shows.
That gives a continuity nothing applied to a finished garment can match: a pattern runs across a side seam and up a sleeve without interruption, because it was never interrupted to begin with.
Because panels are cut from an arbitrary position on the roll, the design has to look right no matter where it is cut. A seamless repeating pattern does this by definition and is what the method is built around.
A single large motif is possible but demanding: it has to survive being cut at an unpredictable point, and the pieces on either side of a seam will not align perfectly, since cutting and sewing are done by hand. Keep focal elements away from where seams will fall, or design so that any crop still reads as intentional.
Extend artwork fully to the edges of the template. Anything left uncovered becomes unprinted cloth once the panel is cut.
The abbreviation DTF always means Direct-to-Film — printing a design onto a transfer film and heat-pressing it onto a finished item. It is a completely different process on a completely different set of products, and its design rules are almost the opposite of these: a bounded print area, a transparent background, a bold graphic that sits on the surface.
If you are designing a chest graphic for a t-shirt, you want the Direct-to-Film guide. If you are designing a pattern that covers a whole garment, you are in the right place.