Best Serger Hems for Thin Knit Fabrics

Hey, congrats on your interest in serger hems for thin knit fabrics!

Sergers (aka, overlockers) have a long-standing love affair with knit fabrics, even lightweight knit fabrics. On garment interiors, these machines make professional-looking, stretchy seams for maximum flexibility and comfort.

Sergers also can be used for hemming knits, giving a handmade-not-homemade vibe to the exterior of your FASHUNS as well. Let’s find out how!

This article is split into a few parts:

1.) Tools for serger hems

2.) Tips for making knit hems with a serger

3.) Serger hem types — tested and photographed

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RELATED: Beginner Serger Supplies: What You Need for a New Serger

Tools for Serger Hems

Let’s assume you already have a serger to work with. Beyond that specialized sewing machine, here are the sewing supplies I employ to create serger hems. (You’ll see they are *somewhat* similar to the tools I suggest when hemming lightweight knits on a sewing machine.)

Starch

Fabrics with body (ody-ody-ody) are less likely to be chewed up in a serger. So, give your lightweight knit more heft with starch. I was all over the spray starch while testing serger stitches for this article. I liked the stiffness of the fabric best when I:

• Used very little starch
• Let the starch soak in
• Didn’t use steam with my iron

Iron and Press Cloth

My folded serger hems turned out best when I gave the fabric a gentle pre-press to set the shape. Don’t go too hot, and use a press cloth to protect delicate knit fabric. Spandex in many knit fabrics can be damaged by heat.

Different Threads

Polyester serger thread on cones works great for knit hems. But, to be sassy, I switched out poly thread for puffy, fluffy nylon thread in the looper (specifically the visible-from-the-right-side upper looper). Different thread types give different decorative looks. A shiny rayon thread would be nice, too.

Some threads call for alternate threading instructions (and tension and presser foot pressure, etc.). For example, I used a thread cradle to pull puffy nylon thread through the looper slot; my serger has a thread air-feed system, and the blast of air can’t send fluffy thread through the path. As always, consult your serger’s manual.

Blind Hem Foot

Did you know you can create a (not-so) blind hem with a serger using a two-thread flatlock stitch? (I explain a little deeper into the article; keep going!) And, while you *can* use a standard overlocker presser foot to make this stitch, you’ll get the best results with a blind hem presser foot for a serger.

Hump Jumper

Whether you call it a hump jumper, bulky seam jumper, or jean-a-ma-jig, we’re talking about a doo-dad that does the same thing: It’s a wedge that you stick under the presser foot to make it flat as it passes over fabric.

Hump jumpers normally are used for thick spots that cause the presser foot toe (and heel) to point up. But, you also can use a hump jumper to keep the beginning and ending edges of lightweight fabrics EVEN — not stretched out or mashed up — as they pass under the foot.

Place the tool under the HEEL when starting a line of serging to prevent jammed-up, uneven stitches.

Place the tool under the TOE when ending a line of serging to prevent stretched out fabric.

Basically, lightweight knits with little/no body need help with their transitions under the presser foot. A hump jumper eases those transitions by raising the presser foot and allowing the feed dogs to do their thing.

RELATED: How Do I Choose a Knit Fabric?

Tips for Serger Hems Before You Get Started

Test, Test, and Test Some More

Picking overlocker stitches out of a thin knit is a huge bummer — like a skip-it-and-start-over-level bummer. To avoid this fate when working with a new-to-you lightweight knit, experiment with:

Tension

Changing up the tensions on loopers and needles can yield different results. For example, a loose upper looper and a tight(er) lower looper could be good for a rolled hem, because the tight(er) lower looper pulls down on the loose upper looper, rolling the edge to the wrong side. Use your sewing intuition and knowledge of how serger stitches come together to fiddle with tension.

My Baby Lock Imagine serger makes auto adjustments to tension to keep stitches balanced. (There is a screw I can tighten to adjust looper tension.) When I want stitches OUT of balance (and I’ve already played with the screw), I use Scotch tape to prevent thread from passing through the tension discs (to make it loose), or I place tape atop the threads’ path to increase friction (to make it tight). I learned this from an online serger class with Jennifer Stern on PatternReview.com.

Differential Feed

Overlockers can be adjusted to feed fabric at different speeds. A high speed is less likely to stretch fabric vs. a slow speed. Try differential speeds of greater than 1 — when the upper and lower feed dogs move at the same speed — for super-stretchy lightweight knits.

Stitch Lengths and Widths

Your manual gives you widths and lengths for all stitch settings. As long as you don’t cause your needle to break OR create questionable noises to come from your serger, you’re allowed to go off manual with your settings. Switch up your width and length and turn the handwheel a few times to make sure your adjustments don’t cause damage. Then, it’s motor time, baby!

Presser Foot Pressure

The force coming down on the fabric could need tweaking, too.

Think About Construction

Controversial idea alert: Maybe think about doing your hems before doing the side seams? Sergers are easier to use on flat — start at the top and serge to the bottom — vs. joined — start at this point and serge in a circle back to the starting point — fabric pattern pieces.

Serge Slowly

Hems are a finishing touch. Don’t rush through them. Serge a little bit, stop, reposition, repeat. This is my serging style. FYI, I sometimes save my hems for a later sewing sesh all together when I’m feeling fresher.

Beware of Knits That Roll

The edges of some knits, particularly single knits, roll up. Keep this in mind if you choose to apply an overlock finish to the edge of your garment. Test to see what happens; could look cool OR not.

Try Less Dense Stitches

Short and narrow stitches are great for fabrics with a lot of body. They’re dicier for thin knits that don’t have much in the way of a “backbone.” There’s not a lot for a dense stitch to anchor to, ya know? Give a longer, wider stitch setting a go.

RELATED: Easy Fabrics to Sew: 8 Forgiving Fabrics

Serger Hem Types for Lightweight Knits

The following overlocker hem treatments are the ones I found the most success with. They were tested on a drapey bamboo-rayon knit (which was featured in a post comparing knit and woven fabrics) that I hit with a touch of spray starch.

For our collective edification, I tested many of the same stitches with different widths, lengths, differential feeds, and thread types. The stitches I am most likely to use are marked with three blue hearts — 💙💙💙.

4-Thread Overlock – Change Differential Feed

• Polyester thread
• 3.5 length, 7 width
• Fabric passed along the blade to “make dust” (insignificant amount trimmed off).

Top

• Differential feed: Normal (1)
• Notes:

Notice the stretched edge; the ends curl up ever-so slightly.

Bottom

• Differential feed: 1.3 (faster than N)
• Notes:

Not stretched when compared to N differential feed.

4-Thread Overlock – Change Stitch Length

• Polyester thread
• Differential feed: 1.3

Top

• 2.5 length, 7.5 width
• Notes:

2.5 is the shortest recommended length for 4T overlock per my manual. 

Bottom

• 1.5 length, 7.5 width
• Notes:

Looks decorative, but is stretched out. Maybe short length overlock stitches would work with a dissolvable stabilizer? The shorter stitches are surprisingly even.

3-Thread Narrow Overlock – Change Differential Feed

• Polyester thread
• 3.5 length, 3 width
• Fabric passed along the blade to “make dust” (insignificant amount trimmed off).

Top

• Differential feed: Normal (1)
• Notes:

Slightly stretched, curled edge. 3T overlock feels less decorative, intentional vs. 4T overlock.

Bottom

• Differential feed: 1.3
• Notes:

Not stretched vs. N differential feed. Less decorative.

3-Thread Narrow Overlock – Change Stitch Length

• Polyester thread
• Differential feed: 1.3

Top

• 2.5 length, 3 width
• Notes:

This is the shortest recommended length for this stitch, per the manual.

Bottom

• 1.5 length, 3 width
• Notes:

Looks decorative, but the edge is stretched.

4-Thread Overlock – Fluffy Nylon Thread + Change Stitch Length

• Puffy nylon thread in upper looper
• Differential feed: 1.3

Top 💙💙💙

• 2.5 length, 7.5 width
• Notes:

This is the shortest recommended length for 4T overlock. Puffy nylon thread looks more full and deliberate vs. poly thread. I would use this serger stitch treatment on a knit if I were committed to having a hem that wasn’t turned or rolled.

Bottom

• 1.5 length, 7.5 width
• Notes:

Upper looper puffy thread is dense — almost looks like piping at a glance. The edge is stretched out.

I think it would be hard to NOT stretch out a thin knit with a stitch this short and dense. A dense stitch calls for fabric with body, and this aint it.

Looks cool, though — so, maybe if you had a gentle hand and didn’t care if the edge stretched.

3-Thread Narrow Overlock – Fluffy Nylon Thread + Change Stitch Length

• Puffy nylon thread in upper looper
• Differential feed: 1.3

Top

• 2.5 length, 3 width
• Notes:

This is the shortest recommended length for 3T narrow overlock. Fluffier thread fills up more of the edge vs. wider 4T overlock with puffy thread.

Bottom

• 1.5 length, 3 width
• Notes

Very dense appearance. Slightly stretched edge.

3-Thread Rolled Hem – Change Looper Tension

• Polyester thread
• Differential feed: 1.8

Top 💙💙💙

• 1.5 length, 3 width
• Notes: 

Increased tension of loopers by one-quarter turn with my serger’s looper thread fine-tuning screw. I would use this stitch for the hems of a “dressy/fancy” T-shirt.

Bottom

• 1.5 length, 3 width
• Notes:

I reduced the looper tension to normal (N) setting. I found the loops and stitches to be less even and the roll to the wrong side wasn’t as tight vs. same stitch with tighter loopers.

2-Thread Wide Flatlock “Blind” Hem 💙💙💙

• Polyester thread
• 4 length, 7.5 width
• Differential feed: 1.3
• Blind hem foot
• Notes:

I pressed up the hem and folded it back, blind-hem style, to create a “ledge.” The ledge needs to be a strong quarter-inch wide for flatlock stitches. (I trimmed off about one-eighth inches with the upper serger blade.)

I adjusted the width of the blind hem foot so that the guide for the edge of the fabric fold was a little shy of one-eighth inches from the needle. This is a big “bite” into the fold of the fabric — much bigger than if I wanted the exterior thread to truly be invisible.

The big bite makes the needle thread (“ladder” stitches on the right side) pretty loose. I think this helps the fabric to lie flat when the line of stitching is pulled open.

To prevent the first few stitches from getting mashed/being too short, I placed a hump jumper under the BACK of the presser foot so that it was the same height as (or higher than) the FRONT of the presser foot. Then I took the first few stitches with the hand wheel. The fabric passed under it without issue.

Used a hump jumper when FINISHING stitches, too, so that the presser foot stayed level. I put the hump jumper under the FRONT of the presser foot to allow the final stitches to pass under without the fabric stretching.

I think this hem works best on individual pattern pieces with straight hems that are sewn together LATER (i.e., hem first, side seams second).

I would use this serger hem if I wanted more body at the hem.

This hem can be reversed to put the flatlock stitches on the right side (and the ladder on the inside).

3-Thread Rolled “Lettuce” Hem

• Polyester thread
• 5 width, 2 length (rolled hem setting)
• Differential feed: 0.6
• Notes:

The idea here is to stretch the fabric while the edge is being serged. I had mixed success with making the edge super wavy. Definitely calls for tests before you create a lettuce hem on your final garment. (Yeah, my lettuce hem didn’t turn out great, LOL.)

Also, make sure you’re making the lettuce hem on the cross grain or bias edge of fabric. The grain edge doesn’t yield many waves; it’s too strong.

RELATED: Sergercore Inspiration for a DIY T-Shirt

Closing Thoughts on Serger Hems for Light Knit Fabrics

The above overlocker settings for hemming are good jumping off points for YOUR experiments.

The No. 1 thing to remember from this post is that to get the results you want, be prepared to test, test, and test some more. I made so many serged hem samples, you guys. SO. MANY.

But now, when I want to serge a hem on a thin knit, I have this “cheat sheet” that literally saves me hours of (less-than-exciting) stitch tests.

To jump-start your own tests, why don’t you download Sie Macht’s Cass T-shirt, which is designed for drapey knits, and try different serger hems on it? It’s a relaxed fit T that’s only three pattern pieces, so it sews up fast. It accommodates busts up to 66 inches and hips up to 70 inches. 

If you’d like to check out more articles that could help you sew a Cass T-shirt (or other T-shirts), I’ve got you covered:

There you go; go forth and serge sleeve and bottom hems on those slinky knits. You can end up with RTW finishes — if you unlock the perfect combo for YOUR project. Good luck!

Over to you: What’s your fave overlock hem treatment? Did I miss any choice options? What other questions do you have about serging hems? Please share in comments! Thanks for reading.