Underlay stitches are a preparatory layer of stitching placed before the visible fill stitches. They're invisible in the finished design but critical to its quality. Underlay stabilises the fabric surface, compresses pile on textured fabrics, and gives the top stitches something solid to sit on. Designs without underlay look flat, sink into the fabric, and are more likely to pucker.
The Three Main Underlay Types
1. Running Stitch Underlay
A single line of running stitches placed around the perimeter or through the centre of a fill area. The most basic underlay type — used for simple shapes, small lettering, and as a minimal stabilisation pass.
2. Zigzag (Lattice) Underlay
A grid of criss-crossing stitches that covers the entire fill area. This compresses the fabric surface evenly and provides a woven base for the top stitches. The most common general-purpose underlay for fill regions.
3. Edge-Run (Contour) Underlay
Running stitches placed precisely along the edges of a fill region. They define the design boundary before the fill is placed, preventing 'bleed' where stitches extend outside the intended shape.
Why Underlay Matters on Different Fabrics
| Fabric | Key Underlay Need | Recommended Type |
|---|---|---|
| Smooth cotton / woven | Light stabilisation | Edge run + centre run |
| Knit / jersey | Strong stabilisation against stretch | Zigzag lattice |
| Fleece | Flatten pile, prevent sinking | Double zigzag |
| Terry cloth | Compress loops, define edges | Zigzag + edge run |
| Denim | Penetrate weave, stabilise surface | Zigzag lattice |
| Velvet / velour | Flatten pile for readable stitches | Double zigzag + edge run |
| Cap front | Compress stiff backing, stabilise foam | Zigzag lattice |
Underlay for Lettering
Lettering and small text needs precise edge definition more than bulk stabilisation. For satin-stitch letters (the typical method for embroidered text), a centre-run underlay placed along the spine of each letter provides the base for the satin columns to sit on without sinking into the fabric.
- •Large text (10 mm+): centre-run underlay along each letter stroke.
- •Medium text (6–10 mm): edge-run underlay around letter outlines.
- •Small text (under 6 mm): running stitch underlay only — additional underlay bulk can obscure fine letterforms.
Common Underlay Mistakes
- •No underlay at all: top stitches sink into fabric, design looks flat or gappy.
- •Underlay too dense: stitches show through the top fill, affecting colour and creating a rough surface.
- •Wrong direction: underlay should typically run at 90° to the top fill for maximum support.
- •Underlay extends outside the fill boundary: clean underlay should be contained within the design shape.
SewFlow includes appropriate underlay automatically:
Open Image to Embroidery →Key Insight
When a design looks 'flat' or the fill colours look dull after stitching, the most common cause is insufficient underlay — not density. Adding proper underlay to a design makes colours pop because the top stitches sit above the fabric surface rather than sinking into it.