Underlay is the light layer of stitches that gets covered by the topstitching; it serves an important role in the embroidery process.

Underlay tacks the fabric to the backing, stabilizes the fabric, helps to reduce the pull effect, raises the top stitches off the fabric and improves the overall look of the embroidery. The underlay you select depends on the fabric that you are stitching on to and also the size and shape of the object.

For a reference on underlay, see your Wilcom ES User Manual.

Types:  You have a number of choices for automatic underlay including the option to apply 2 layers of underlay, either the same type or 2 different types.

Center Run – for stability and clean, straight narrow columns.
Zigzag – for wider columns to add loft.
Double Zigzag – for wider columns to add more loft.
Edge Run – to stabilize the outer edge of the object boundary.
Tatami – for large areas with a Tatami cover stitching.

When:  In most cases you will want to use some type of underlay.  Knowing the type of fabric and backing being used as well as the stitch type will help determine which type(s) of underlay to use and when.

Where do I use Underlay?

General guidelines

Narrow columns and small areas – Center Run for stability.
Wider satin letters – zigzag or double zigzag for loft.
Lettering on Fleece or Toweling – Edge Run and double Zigzag to flatten the pile.
Large open fill areas – 2 Tatami underlays (angles at 45 and 135 degrees) this will stabilize fabrics such as polo shirts and t-shirts and if using a high pile fabric like towelling to flatten the pile.

Underlay Guidelines:

7mm letters – With narrow columns that occur with small lettering, it is important to use a center run underlay, if you choose to use any underlay.  Make sure that you have the center run underlay set to a smaller stitch length, like 1.8-2.2mm, and that variable run length is selected.  The variable run length fill forces the running stitches to hug the curve on letters like O and S.
12mm letters – Look at the width of the satin stitches that make up the letters.  Some alphabets at 12mm have very narrow columns; others are a bit wider.  With the wider columns you can use zigzag or double zigzag to add the look of density and loft to the lettering.  With the narrower lettering styles, stick with the center run underlay.
20mm letters – Watch the width of the column on letters this size, but with most alphabets, the column will be wide enough to warrant edge run, zigzag, double zigzag or a combination of edge run and one of the zigzag choices.  With larger letters (wider satin stitches) you need the added underlay for stability and thread coverage.
Large fill areas (with a Tatami fill stitch) – With larger areas you will need to have more underlay to tack the fabric to the backing and help prevent too much push and pull of the fabric, which can effect registration.  You will want to put at least one layer of a tatami underlay at 90 degrees to the top stitch angle to properly tack the fabric to the backing.  You can adjust the stitch spacing of the underlay for more coverage on high contrast applications, like dark thread on a light garment.  If you need even more coverage, like with high pile fabrics such as thick sweatshirts, towels, or fleece, you can use 2 layers of tatami underlay.  Set the first layer at 45 degree to the stitch angle and the other at 135 degrees.  This will not only stabilize the area and hold down the pile, it will add more thread coverage to the area, making it look denser without adding additional density to the top stitching.

Take into consideration the fabric, backing and size of the area that you are applying the underlay. Remember underlay, although not seen on the final sew out, plays an important part in making high quality embroidery.

Source: embroiderystartup.com