Ask ten people what makes a logo stitch out clean and most will say thread, tension or stabilizer. Those matter, but some of the biggest work happens before you see a single top stitch. It's the underlay: the layer of stitches the machine lays down first, which ends up hidden under the finished design.
After more than two decades of digitizing, I'd say underlay is the one setting that most often separates a file that stitches beautifully from one that puckers, gaps or looks thin. Here is what it does, the main types, and when each one is the right choice.
What is underlay in embroidery?
Underlay is a foundation of low-density stitches placed under satin columns and fill areas. It has three jobs:
- Lock the fabric to the stabilizer so the top stitches don't drag the fabric around.
- Flatten the surface so pile, nap or texture (towels, fleece, piqué) doesn't poke through the top stitching.
- Give the top stitches loft and a clean edge, so satins look full and rounded instead of flat and sunken.
Underlay is part of the design file. It's not the same thing as stabilizer, which is the material you hoop behind the fabric. You need both: stabilizer supports the fabric, underlay anchors the stitches to it.
The main types of underlay
1. Center run (center walk)
A single running stitch down the middle of a satin column. It's the lightest option, used for narrow columns roughly 1–2.5 mm wide, such as small lettering and thin outlines. On anything narrower than about 1 mm, most digitizers skip underlay entirely, because there's no room for it without making the column lumpy.
2. Edge run (contour or edge walk)
A running stitch that travels around the shape just inside the edge, typically inset about 0.3–0.5 mm. It defines crisp edges and holds the fabric along the borders of the shape. Edge run is the workhorse for medium satin columns, roughly 2.5–4 mm, and it's the base for most fills too.
3. Zigzag
An open zigzag stitched back and forth inside the column, usually at a spacing of around 2 mm. It adds loft and covers more of the fabric surface. Zigzag is used on wider satins (about 4 mm and up), usually on top of an edge run. A double zigzag, which runs out and back, is used where the fabric has a lot of texture.
4. Fill (tatami) underlay
For larger fill areas, the underlay is itself a light fill with wide row spacing, often around 2–4 mm, stitched at an angle to the top fill, commonly 90 degrees. Crossing the directions spreads the pull across the fabric instead of all in one direction. Edge run plus a light tatami underlay is a common combination for a filled logo.
5. Lattice or double tatami
Two fill underlays at crossing angles. This is the heavy-duty option for terry towels, fleece and thick knits, where the pile would otherwise swallow the stitches.
Which underlay to use: a quick guide
- Satin under about 2.5 mm: center run, or none for very fine detail.
- Satin about 2.5–4 mm: edge run.
- Satin over about 4 mm: edge run plus zigzag. Columns wider than around 7–8 mm are usually split or turned into fill.
- Small fills: edge run, sometimes nothing extra.
- Large fills: edge run plus a light tatami underlay at a different angle.
- Towels and fleece: heavier underlay (double zigzag or lattice) plus water-soluble topping on top of the fabric.
These are starting points, not fixed rules. The fabric decides how far up or down you go.
How fabric changes the underlay
- Thin T-shirts and performance knits: keep it light. Too much underlay plus a full top layer makes a stiff patch and pulls the knit. An edge run and a light fill underlay is usually enough.
- Piqué polos: the textured weave shows through thin stitching, so they need a solid underlay under fills and satins.
- Caps: structured caps need underlay that locks the front panels down, stitched from the center outward so the fabric doesn't bubble toward the sides. We go deeper on this in how to digitize a logo for a hat.
- Leather and vinyl: every needle hole is a permanent perforation. Use minimal underlay and lower density so the material isn't cut.
- Denim and twill: stable fabrics that tolerate standard underlay well.
Signs your design has the wrong underlay
You can often diagnose an underlay problem just by looking at a stitch-out:
- Puckering around shapes or fabric showing through the top stitches: too little underlay, or the wrong type. See our guide on why embroidery puckers for the other causes to rule out.
- Gaps between outlines and fills: the fabric moved during stitching. Better underlay (and correct pull compensation) holds it in place.
- Underlay peeking out at the edges: the inset is too small, or the column was narrowed without adjusting the underlay.
- Stiff, board-like embroidery, or frequent thread breaks: too much underlay stacked under an already dense top layer.
- Lumpy small text: underlay on letters that are too small for it. Letters under about 5 mm tall usually need only a center run, or no underlay at all.
Why auto-converted files often get underlay wrong
Auto-digitizing software tends to apply one underlay setting to every object, or none at all. It doesn't know that the 2 mm text needs a center run while the large background fill needs a crossing tatami, or that the shirt is a thin knit rather than a cap. That is why an auto-converted logo can look fine on screen and fall apart on the garment.
A hand digitizer chooses underlay object by object, based on width, size and fabric. If you want a file built that way, our hand-digitized logo service sets underlay for the fabric you tell us about, with no auto-conversion. Designs 6 inches or less are $10, larger ones are $20, and files arrive by email within 12 hours in EMB, DST, PES, JEF, XXX, VP3, SEW, HUS and more. Size changes and tweaks after delivery are free, and if it doesn't stitch right, we re-digitize it until it does. You can read how our digitizing service works before you order.
If you'd rather start with designs that are already digitized and tested, browse our machine embroidery designs, with 600+ files available for instant download.
Quick FAQ
Can I add underlay to a DST or PES file?
Not properly. Stitch files like DST and PES store individual stitches, not objects, so most software can't recalculate underlay in them. Underlay is set in the original working file (such as EMB) or by re-digitizing.
Does underlay increase stitch count?
Yes, usually by a modest amount, since underlay is low density. The trade-off is worth it: a design without enough underlay often needs a second run or a redo.
Does underlay replace stabilizer?
No. Stabilizer supports the fabric during stitching; underlay anchors the stitches to the fabric and stabilizer. Skipping either one causes problems.
Want a logo with underlay built for your fabric? Order custom embroidery digitizing and get your file within 12 hours.