Shedding Light on Your Bobbin Thread Options - Cool Stitches

Shedding Light on Your Bobbin Thread Options

Last evening in our local sewing club meeting we were reviewing sewing machines and overcoming sewing headaches. The subject of the bobbins and threads came up and created quite the discussion! Here is some information to give you confidence in your selections and solutions to issues you may have encountered. 

Let's start with your Bobbin Thread

Your bobbin thread does not need to match the top thread in type and size. The bobbin thread can be a lighter weight than the top thread and still provide sufficient strength without adding bulk.

Using a cotton top thread with a poly bobbin thread is fine. Using a 50 wt. cotton bobbin thread with a 30 wt. cotton top thread will also work. If you want a reversible look to show off decorative thread on both sides, of course it’s fine to use the same thread on top and in the bobbin.

Since the bobbin thread does not go through a needle, there are fewer problems with bobbin threads than with top threads. Most common bobbin threads are cotton, spun poly, cotton-wrapped poly, and filament poly.

  • Cotton: Quilters love it. It keeps the fiber content consistent with the fabric, batting, and top thread. For embroidery, it is okay, but on dense fill designs, cotton bobbin thread will result in a stiff design. Be aware that lower quality cottons produce more lint which in turn requires more frequent machine cleaning. Choose good quality bobbin thread.
  • Spun poly: Stronger than cotton. Many machine quilters like this thread due to its strength. Like cotton, it does not have a slick surface and sometimes tends to grab the top thread too tightly creating uneven stitches and top thread breakage. Choose a type with very low lint.
  • Filament poly (not monofilament): This thread has a shiny appearance and is virtually lint free. It can be thin and lightweight, yet strong. Embroiderers love this thread since it creates a soft backing, even on dense designs. Many machine quilters like using a filament poly thread in the bobbin. Due to its slick surface, it works well with metallic threads and heavy cotton threads. The slickness of the filament poly thread does not snag or grab the top thread. If you’ve had trouble using metallics or heavy cotton threads, a slick bobbin thread may solve some problems.

Sewing machines are factory preset to have the top and bottom thread form even stitches. If the top and bottom threads are identical in fiber and weight, adjustments should not be necessary. However, if we use cotton on top and poly underneath, or metallic on top and poly underneath, or a heavy thread on top and a thin thread underneath, it is necessary to adjust the tension settings. It is fine to use different types and weights on the top and bottom.

Think of the top and bottom thread as having a tug of war. If the threads are identical and you are sewing on a single layer of fabric, both sides have equal strength and the result will be a draw. The sewing should therefore produce perfectly even stitches with no top thread showing underneath and no bobbin thread showing on top. However, in the real world, the teams are rarely equal. One team will be stronger or bigger or faster than the other. We use decorative threads on top.

We often use different fibers for the top and bottom threads. We also add stabilizer or batting. Sometimes we might use a cotton bobbin thread and other times we use a polyester bobbin thread.

All these factors make it necessary to adjust the tension for each project. By adjusting the top tension either tighter or looser, we are able to add or take away strength on the top thread team to equalize the tug of war battle.

Following is a list of things that affect stitch results:

1. Batting: This adds drag on top thread. Cotton batting tends to grab the thread more than poly batting, adding more friction on the thread.

2. Fabric type: Dense fabric puts more stress on the thread.

3. Top thread thickness and type: Metallic is less flexible than cotton or poly. Poly is stronger than either cotton or rayon.

4. Bobbin thread type: Cotton bobbin thread tends to grab more than a silk-like filament poly. Sometimes grabbing is preferred and sometimes it causes problems. A silk-like filament poly thread (not spun poly) in the bobbin will work better with metallic or heavier cotton and spun poly thread because its silk-like finish acts almost like a lubricant, sliding nicely with the thread.

Our next post will continue this discussion as we move to needles, tension, and more to help you understand why things work - or don't - so you can more easily address any sewing headaches you encounter. Thank you to EE Schenck for the information! 

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