Why do seams tear?

Probably everyone knows the sound of a seam tearing. This often happens on the seat seam as you bend down or on the neckline of a top as you pull it over your head while getting dressed. But why do some seams tear so quickly? First of all, in many cases, it is not due to the strength of the sewing thread. The secret is actually in the elasticity of the seam. If the seam is less elastic than the fabric, it tears when the material is stretched. The more elastic a fabric is the more elastic the seam needs to be. For this purpose, A&E Gütermann offers a specific range of sewing threads.

However, the use of elastic sewing threads requires special sewing machine settings. For this very reason, standard sewing threads are often used in the industry even for stretchy fabrics. In this case, alternative methods have to be used to ensure that the seam is sufficiently elastic.

torn seam
How to make a seam stretchy

A key factor in the elasticity of a seam is the thread reserve, i.e. the amount of sewing thread in the seam. The higher the thread reserve in the seam, the more elastic it will be. The thread reserve is essentially determined by the stitch type. More or less thread will be required depending on how the sewing threads are interlaced in the formation of a stitch. For example: the double lockstitch requires at 4 stitches per cm  around 2.8 metres of thread per metre of seam, while the double chain stitch requires around 4.8 metres of thread per metre of seam for the same stitch density. The double chain stitch is therefore much more elastic than the double lockstitch because more thread is available, and is highly recommended when a high seam elasticity is required.
 

Doppelsteppstich               Doppelkettenstich

Double lockstitch                                                Double chain stitch

Depending on the area of application, there are other types of chain stitch apart from the simple double chain stitch, which can also achieve a high seam elasticity due to their high thread reserve. These include overedge stitches, two-needle double chain stitches and covering chain stitches. However, if you really need to use a double lockstitch, even if only for its appearance (e.g. when quilting edges), particular attention must be paid to the stitch density and thread tension in order to achieve sufficient seam elasticity.

Additional tip on double lockstitch seams for highly elastic materials:
A particularly elastic double lockstitch seam can be achieved, for example, when using a highly elastic sewing thread such as Maraflex. This special thread convinces with particularly beautiful double lockstitch seams!

The stitch density is also an important factor when you want to achieve greater flexibility in a seam. The basic principle here is: The higher the stitch density, the more elastic the seam. This is because a higher stitch density results in a higher number of twists, which in turn results in a higher thread reserve in the seam. Depending on the material thickness, the elasticity of the double lockstitch can be increased by around 10% with just one more stitch per cm.


Fadenverschlingung in Nähgutmitte          higher stitch density

Comparison average and increased stitch density

The thread tension is often given little attention in terms of seam elasticity. However, it plays an important role, especially when using the double lockstitch. To achieve the most elastic seam possible requires a balanced distribution of tension and the ideal positioning of the points where the upper and lower threads twist around each other. If the thread tension is not set correctly, i.e. if the twists are not positioned precisely in the centre of the material, the amount of thread on one side will be shortened, the tensile forces cannot be distributed evenly during tensile loading and the seam will tear faster.
 

Fadenverschlingung in Nähgutmitte                Fadenverschlingung nicht in Nähgutmitte

Balanced thread tension at double lockstitch                    Unbalanced thread tension at double lockstitch
 

When setting the thread tension, the quality of the sewing thread also plays an important role. The smoother the sewing thread, the better. This is because sewing threads that are very smooth can be processed with a lower thread tension than uneven threads. Also, since the thread tension is lower, there is more thread in the seam, which makes it more elastic.


Clever tricks for experienced users

In addition to all these factors, there are many other tricks that can be used to achieve particularly uniform, elastic seams. For example through…
 

sewing foot pressureKeep the sewing foot pressure as low as possible, so that the sewing material can be passed evenly under the presser foot during sewing, without seam displacements.

Nähmaschine mit Puller-EinrichtungDepending on the material and the desired application, a puller device can be used for a uniform and controllable feed, which reduces the risk of layer displacements and creates a uniform seam pattern with constant feed.

 


Choosing the right sewing thread is also critical

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We are happy to give you personalised advice about which product is the best for your application. Contact us via naehtechnik@guetermann.com.