Short answer: underlay is the stitching sewn first, under the visible stitches. For satins: a centre run under narrow columns (under about 2.5 mm), an edge run for medium ones, and an edge run plus zigzag for wide ones. For fills: an edge run on small shapes, and an edge run plus tatami (rows at 90° to the top stitching) on anything wider than about 6 mm. Underlay holds the fabric to the backing, lifts the top stitches and stops gaps; pull compensation then widens the top stitches to make up for fabric pull.
Underlay is invisible on a finished piece, which is why it's so often skipped. That's also why so many home-digitized designs sink into the fabric, gap at the edges or pucker. Getting underlay right is one of the clearest differences between amateur and professional files.
What underlay does
- Stabilizes: it stitches the fabric to the backing before anything else, so the fabric can't shift between colours.
- Lifts: it gives the top stitches something to sit on, so they don't sink into piqué, fleece or terry.
- Defines the edge: an edge run marks the shape's outline, so the top stitches have a firm edge to land on.
- Prevents gaps: a well-anchored shape pulls in less, so fills and outlines stay together.
Satin underlay types
| Type | What it is | Use it on |
|---|---|---|
| Centre run | One running line down the middle | Narrow columns, small lettering (under about 2.5 mm) |
| Edge run | A run just inside both edges | Medium columns (about 2.5–5 mm) |
| Zigzag | A loose zigzag across the column | Adding loft; puffy, raised satin |
| Edge run + zigzag | Both | Wide columns (over about 5 mm), borders, caps |
| None | No underlay | 3D puff (underlay would flatten the foam); very small detail |
In EasyDigitizer, Auto (by column width) uses exactly these breakpoints: under 2.5 mm a centre run, under 5 mm an edge run, wider an edge run plus zigzag. The edge run sits 0.4 mm inside the edge with 2 mm stitches, and the zigzag steps 0.7 mm.
Fill underlay types
| Type | What it is | Use it on |
|---|---|---|
| Edge run | A run around the inside of the shape | Small fills (under about 6 mm across) |
| Tatami | Light, open rows at 90° to the top stitching | Holding large fills flat |
| Edge run + tatami | Both | Most fills over 6 mm, and anything on knits and fleece |
| None | No underlay | Motif and very light gradient fills; second layer of a blend |
Auto (by size) chooses an edge run under 6 mm and an edge run plus tatami above it. The tatami underlay rows are about 1.8 mm apart with 2.4 mm stitches, inset 0.8 mm from the edge, so it never peeks out. Open fills change the rule: motif fills get none, and gradient fills get none or only an edge run depending on how light their lightest end is.
Underlay by fabric
- Caps and twill: standard; edge run plus zigzag under satins, plus tatami under fills.
- Piqué polos: don't skip it. Piqué swallows stitches without it.
- Fleece and towels: full underlay, plus a knockdown layer or topping. See digitizing for beanies, fleece and knits.
- Performance wear: lighter. An edge run under fills and a centre run under satins avoid stiffness and puckering.
- Leather: minimal, because every needle hole is permanent.
Pull compensation
Underlay holds the fabric, but thread tension still pulls it in across the stitches. Pull compensation widens each object slightly to make up for it. Set it per object from 0 to 1 mm:
| Fabric | Typical pull comp |
|---|---|
| Woven, twill | 0.20 mm |
| T-shirt knit | 0.35 mm |
| Fleece | 0.40 mm |
| Caps | about 0.30 mm |
Signs it's too low: gaps between a fill and its border, round shapes sewing oval, thin-looking satins. Too high: letters closing up and outlines overshooting the art.
Frequently asked questions
What is underlay in embroidery?
Stitching sewn before the visible stitches, to hold the fabric to the backing and give the top stitches a stable base.
Which underlay should I use for small text?
A centre run. Edge runs and zigzags take up width that small letters don't have.
Does underlay add stitches?
Yes, typically 15–30 % for fills and less for satins. It's what keeps the design from sinking, puckering or gapping, so it's worth it.
When should I use no underlay?
Under 3D puff satin, under open motif and light gradient fills, and on tiny detail where any underlay would show.