Sewing 100wt Thread

Dear readers, I have had an epiphany. It suddenly occurred to me while sewing my newest quilt exactly why something I had been doing for awhile (swapping needles around) was keeping my thread from breaking. It was a literal "Aha!" moment. My newfound state of enlightenment inspired me to write this post in order to share my knowledge with all of you lovely people.

And so, without further ado, this month's blog post is all about sewing with 100wt thread.

It's a love-hate relationship

I've written before about why I sew with 100wt thread. This is the "love" part of our relationship: 100wt threads, such as MicroQuilter and InvisaFil, are next to invisible when sewn into a quilt. Note they are not actually invisible the way MonoPoly — and monofilament — is. 100wt threads are visible if you're standing right next to the quilt, but from even a few feet away, they disappear to the point it's hard to tell the quilt has been sewn at all.

It's for that reason I use 100wt threads. I design my quilts to tell their stories entirely in fabric. I don't want the stitching to distract from the fabric. But, I also put a lot of effort into my stitching, and want it to be seen if someone gets close. It creates an extra, subliminal dimension to my work that I adore. In this respect, 100wt thread is perfect.

Take a look at my quilt, Beauty Queen, below. My gator girl is 48" wide, and when standing back from the quilt, it's almost impossible to tell it was sewn at all. However, an up-close-and-personal look reveals all the pebbled stitching I put into, for example, the leathery texture of her face.

Beauty Queen Stitching

The "hate" part of my relationship with 100wt thread has to do with how difficult it is to sew. It's such a thin thread that it has very little strength (compared to thicker threads), and is therefore much more delicate. It's very sensitive to the slightest changes in tension, needle size, stitch length, sewing speed, movement of the fabric, etc. If the sewing conditions aren't perfect, the 100wt thread will fray or break.

For me, the most frustrating thing was not understanding why the thread was breaking. There are so many possible factors and variables, and the thread is so incredibly sensitive. More than once, I've set my sewing area and machine to (what I thought were) the perfect settings and still had my thread break every 6" or so. That's INFURIATING.

Practice does make perfect

I have been using 100wt thread on my quilts from the very first quilt I made, and actually taught myself how to quilt with it from the beginning. (For the record, that is not an experience I'd recommend. If you're just learning how to quilt, start with a 40wt polyester thread, like Master Quilter. You will have a much easier time learning the basics.)

As of writing this blog post, I have been using 100wt thread almost exclusively for two and a half years. It's gotten easier, and I have gotten much better, at working with the thread without it fraying or breaking. I've been intuitively making changes and adjustments on the fly, but the reason why those changes were working finally clicked in my brain. That was my "Aha!" moment.

My Epiphany

This realization felt so monumental to me that it warrants its own section in this post.

I realized that I was switching needles when sewing over different areas of my quilt. Specifically, I was switching to smaller needles when sewing over the thickest areas. Basically, the more layers of fabric I had to sew through, the skinnier the needle had to be to keep the thread intact.

Absolutely nowhere is the relationship between needle size and quilt thickness written down. There are guides that recommend using 60/8, 70/10, 80/12 microtex needles with 100wt thread, but not why three different sizes are needed or when to switch. Now that I've had this realization, I'll always know whether to try a thinner or thicker needle based on the thickness of the quilt I'm trying to sew without trying other sizes willy nilly and hoping for the best.

Kestrel's Guide to Sewing with 100wt Thread

To wrap up this post, I want to share the knowledge I've gained about how to successfully sew with 100wt threads. Sewing machines are fickle creatures and each has its own personality, so what has worked for me may not perfectly work for you. However, hopefully I'll be able to give you a starting point at the very least.

Kestrel's Sewing Machine

I use a Bernina 790 Plus.


My machine prefers InfisaFil to MicroQuilter. I honestly have no idea why, as they're both very high quality, 100wt threads.

InvisaFil Cheat Sheet

Wonderfil, InvisaFil's manufacturer, has published Hints & Tips sheets for sewing with all their threads. This is the Hints & Tips sheet for InvisaFil .

Thread Tension

My machine defaults to 4 for FMQ, but I typically sew with 3.5 for 100wt thread. It's slightly less pressure that still keeps the thread loops hidden in the quilt sandwich (no top thread on the back nor bobbin thread on top). However, I have come across two spools of InvisaFil that had to be sewn with a tension of 2 in order to hide the loops. Keep an eye on your threads and don't be afraid to adjust the tension if need-be.

The thread tension should be the first thing you figure out when sewing with 100wt thread. Practice sewing on a quilt sandwich and adjust the tension until the loops are cleanly tucked within. Figuring out what the tension should be will eliminate one variable when troubleshooting breaking thread.

Bobbin Thread

Use InvisaFil in the bobbin, too. I've had the most success when my top thread matches the bobbin thread. It's also easier to adjust thread tension.

Edit 11-02-2020: After talking with several other people who sew with 100wt thread, it seems that each machine has a different preference. If you're having trouble, try different thread weights (100wt, 80wt, 60wt, and 40wt) in the bobbin to see if that helps. Keep in mind that changing the bobbin thread will require you to re-adjust your thread tension.

Stitch Length

The cheat sheet says stitches should be 1.0-1.5 in length. My machine's default is 2, so I've left it there and it's working fine for me.

Presser Foot & Pressure

I use the Bernina Stitch Regulator with the open toe. Any hopping-style foot for free-motion quilting should work just fine.

I leave the presser foot pressure on the default 50. I experimented with less pressure but didn't see a quantifiable result.

Sewing Speed

I quite often sew as fast as my machine will allow — the stitch regulator beeps at me if I'm moving the fabric too fast. It's most important to move your fabric at a consistent speed, whether fast or slow, even with a stitch regulator. Consistency > Speed.


Keep in mind that my layers of fabric will probably be stiffer than yours because my fabric is all treated with diluted Mod Podge to prevent fraying. This means my fabric is more rigid and less giving to the thread. You will need to experiment with your own machine to see what size needle works for various thicknesses of quilt sandwich.

When to Change Needles

When sewing with regular needles (not titanium-coated), I use a new needle each day at minimum. You should change your needle every 6-8 hours of sewing. Titanium-coated needles will last significantly longer.

If the thread breaks, as in snaps more-or-less cleanly at one point, I've found that means I was moving the fabric too fast or inconsistently. The needle is probably fine. Just re-thread the machine and keep going.

If the thread frays, as in the thread is still kind of intact but one or more plies have come undone, that indicates a problem with the needle. The needle itself might have an issue (like a bur or it's dull), or you need a different size. Either way, time to change needles.

When sewing a quilt, I just keep going until I have a problem. If my 80/12 needle is sewing through 10 layers of fabric without issue, I don't question it. As soon as the thread frays, though, I stop, tie off, tuck, change needles, re-thread, and start again.

Test Stitching

I've found my machine is far more forgiving when sewing in small increments with lots of changes in direction (such as pebbles or stippling patterns). I run into the most problems on long, straight areas. Make sure you test both to make sure your machine will handle a variety of stitching styles.

If All Else Fails

If you're still struggling to make a 100wt thread work for you, but like the next-to-invisible look, try DecoBob . DecoBob is an 80wt polyester thread. It will be a little more forgiving than InvisaFil since it's slightly thicker, but will still be almost invisible on your quilt.

Update: 06-02-2021


Keep your sewing machine well-lubricated. My 790 likes new lubricant every 6-8 hours of sewing. If it's been a while since I've used it last, I'll use an extra dab of oil before getting started. This really helps the thread run smoothly through the mechanisms.