Underlay

Underlay is the unseen scaffold beneath every well-digitized embroidery. Before the satin or fill that the viewer actually sees, the machine first lays down a sparse network of run stitches that grip the fabric, hold the stabilizer in place, and create a slight raised platform for the top thread to sit on.

There are several underlay styles, each chosen for a specific purpose. Edge-run underlay places stitches just inside the perimeter of a shape to lock the fabric down before the satin fills the column. Zigzag underlay alternates side to side across a column to add lift on plush or knit fabrics. Parallel underlay runs straight lines across a fill area, perpendicular to the top stitches, to flatten and stabilize. Center-walk underlay travels down the centerline of a satin column to control fabric pull.

Without underlay, embroidery on knit and plush fabrics sinks into the substrate, the edges look soft and fuzzy, and the design puckers as the top stitches pull the fabric in. A polo or pique knit absolutely requires underlay. A heavy twill jacket can sometimes skip it on small shapes. Hats and caps need extra underlay because the curved foam crown moves under the needle.

A digitizer chooses underlay type, density, stitch length, and inset from the shape edge based on the fabric and the shape size. Underlay is invisible to the customer but is one of the clearest tells of a skilled digitizer. Cheap auto-digitized files often have no underlay at all, which is why they pucker on real garments.