Embroidery underlay is a layer of light stitches sewn before the visible top stitches. It holds the fabric to the stabilizer, stops the fabric shifting while the design sews, and gives the top stitches a base so they don't sink into a knit or a towel's pile. The four common types are center run, edge run, zigzag and tatami. Narrow shapes need a little underlay; wide satins and large fills need more.
What underlay does
You don't see underlay in a finished design, but you see what happens without it. Satin edges go wavy, fills look thin and patchy, fabric shows through, and shapes sink into soft fabric. Underlay handles four jobs:
- Stability. It locks the fabric to the stabilizer before the dense stitching starts, so the fabric can't creep.
- Loft. It lifts the top stitches above textured fabric such as piqué, fleece and terry, so they look full and smooth.
- Clean edges. Underlay that runs just inside a shape's outline gives satin stitches a firm edge to wrap over.
- Coverage. A base layer helps hide the fabric under the top stitches without making the top layer heavier.
Underlay also works hand in hand with pull compensation. Fabric that's anchored before the top stitches start pulls in less, so shapes hold their size better.
The four types of underlay in embroidery
| Type | What it is | Typically used for |
|---|---|---|
| Center run | A single line of running stitch down the middle of a column | Narrow satins, roughly 1 to 2 mm wide, and small lettering |
| Edge run | Running stitches just inside the edges of a shape | Medium satins, lettering and borders; also around fill shapes |
| Zigzag | An open zigzag inside a column, like a very light satin | Wider satins, roughly 3 mm and up, especially on knits |
| Tatami | Widely spaced rows of fill, usually at an angle to the top fill | Large fill areas |
Center run underlay
Center run is the lightest option: one pass of running stitch down the middle of a satin column. It tacks the fabric down without adding bulk. That makes it the usual choice for narrow columns and small text, where heavier underlay would make letters lumpy or poke out at the sides.
Edge run underlay
Edge run (also called edge walk or contour underlay) traces the inside of a shape, typically set in a few tenths of a millimeter from the edge so it doesn't peek out. It gives satin stitches a crisp line to wrap over and helps lettering keep its shape. On its own it suits medium satins. On wider columns it's usually paired with zigzag.
Zigzag underlay
Zigzag underlay sews an open zigzag across the column, spaced far more widely than the satin on top. It adds loft and coverage, so wide satins look full instead of flat. A double zigzag, two passes that cross each other, is a common choice for heavy or stretchy fabrics.
Tatami underlay
Tatami underlay is a loose fill sewn under a large fill area. Its rows usually run at a wide angle to the top fill, often close to 90 degrees, so the two layers cross and hold the fabric in both directions. It's what stops large fills from gapping, shifting or showing fabric through, especially on knits. For when a shape gets fill rather than satin in the first place, see satin vs fill stitch.
Choosing underlay by fabric
The fabric decides how much underlay a design needs. As a rough guide:
| Fabric | Underlay approach |
|---|---|
| Stable wovens (twill, denim, canvas) | Standard: center or edge run under satins, a light tatami under large fills |
| Knits (t-shirts, polos, hoodies) | Stronger: edge run plus zigzag under satins, full tatami under fills, with a cut-away stabilizer |
| Caps | Firm underlay to hold the design on the curve, sewn from the center outward |
| Towels and fleece | Heaviest: enough to flatten the pile, plus a water-soluble topping on top |
| Light fabrics (linen, silk, quilting cotton) | Light: too much underlay stiffens thin fabric and makes it pucker |
More underlay isn't always better. Every layer adds stitches, stiffness and run time. Stack heavy underlay under a dense top layer and a soft polo logo starts to feel like a patch. Match the underlay to the shape's width and the fabric, and no more.
Common underlay problems and fixes
- Underlay showing at the edges. It isn't set in far enough from the outline, or the top stitches pulled in. Inset it more or add pull compensation.
- Satins look flat or sink on knits. Not enough underlay. Add zigzag under wide columns.
- Small text looks lumpy. Too much underlay under narrow strokes. Use center run only, or none on the tiniest strokes.
- Fabric shows through a large fill. The tatami underlay is missing or too light, or the fabric shifted. Add tatami underlay and check the stabilizer.
- The design feels stiff as cardboard. Too much underlay plus too much density. Lighten one or both.
How SatinSmith handles underlay
SatinSmith adds underlay under everything automatically, so you don't set underlay types stitch by stitch. Instead, you pick a fabric preset in the Fabric panel. Knit and Towel get stronger underlay and more pull compensation so shapes don't shrink or sink. Cap sews from the center outward. Light gets a lighter fill so thin fabrics don't pucker. Our fabric settings guide explains which preset fits which garment.
Switch presets and the design is stitched again with the new settings, and the stitch count in Details updates to match. The density map in the View menu marks thick spots in amber and red, which is where too much underlay under a dense top layer shows up. Reading the stitch preview and checks covers the rest. As always, a test sew-out on the real fabric and stabilizer is the final check.
Questions
What is underlay in embroidery?
Underlay is a layer of light stitches sewn before the visible stitches of each shape. It anchors the fabric to the stabilizer, lifts the top stitches above textured fabric, and gives satin edges a firm base. You don't see it in the finished design, but it decides how clean the design looks.
Do all embroidery designs need underlay?
Nearly all satins and fills do. Very small details and running stitch outlines usually don't, and very narrow text may only get a center run. Skipping underlay on larger shapes is a common cause of gaps and wavy edges.
What's the best underlay for t-shirts?
Knits need more support: edge run plus zigzag under satins, and tatami under fills. Pair it with a cut-away stabilizer so the fabric can't stretch as it sews. In SatinSmith, the Knit preset handles this for you.
What's the difference between edge run and center run underlay?
Center run is one line of stitching down the middle of a column, used for narrow shapes. Edge run follows the inside edges of a shape, which gives satin stitches a firm, crisp edge. Wider columns often use edge run with zigzag on top.
Can you have too much underlay?
Yes. Too much makes designs stiff, lumpy and slow to sew, and it can peek out at the edges of small lettering. Match the underlay to the shape's width and the fabric.