What is seam puckering?
It is one of the most aggravating and persistent problems encountered while making fine seams in woven or knitted fabrics.
Since the thread is an essential part of any seam, it is often blamed for creating seam pucker. There are, however, other contributing factors which include fabric structure, seam construction, thread/needle size and feeding problems – both mechanical and operator induced.
Occurs due to: incorrect sewing tension
Tension pucker is caused while sewing with too much tension, thereby causing a stretch in the thread. After sewing, the thread relaxes. As it attempts to recover its original length, it gathers up the seam, causing the pucker, which cannot be immediately seen; and may be noticeable at a later stage.
Tension is also referred to as seam shrinkage or thread relaxation pucker.
Test to identify
Carefully cut both the top and bottom threads of all stitches along a few centimetres of the seam, without distorting the thread loops in the fabric. If the pucker is relieved over this length, then it was caused by thread tensions.
• Reduce the tension applied to the thread while it is being wound onto the lock stitch bobbin.
• Set the needle thread tension to be as light as possible while achieving a balanced stitch at the same time. This will reduce the amount of puckering while the thread is stretched and improve the sewability.
• Use a high-quality sewing thread with a low-friction lubricant applied to it. This will allow the thread to run smoothly through the thread guides and tension controls.
• Use a high-quality sewing thread with even unwinding tension for smooth flow of thread to the sewing area.
• Ensure that the sewing machine feed timing is correctly set, as incorrect feed timing can lead to the need to apply excessive tension to the needle thread. Incorrect timing may lead to an imbalanced stitch.
Occurs due to: structural jamming
If the fabric is densely woven, there may be insufficient space to accommodate a sewing thread without distorting the woven yarns. Stitching along a straight line will distort and stretch the adjacent fabric yarn(s), setting up stresses which cause the seam to pucker. This is known as structural jamming or inherent pucker.
The severity of this condition depends primarily on the characteristics of the fabric fibre, the closeness of the weave or knit and the fabric finish.
Relatively coarse fabrics of natural fibres are less likely to experience inherent pucker than tightly woven synthetics, delicate microfibres or fabric with pucker-sensitive finishes or treatments.
Test to identify
Carefully cut and remove the stitches in a short length of the seam, after first checking for the tension pucker. If both faces of the seam revert to a smooth surface, structural jamming has occurred.
• Cut and sew on the bias when possible. By sewing at a biased angle, the needle displaces different sets of wrap and weft yarns, thereby significantly reducing the incidence of pucker.
• Opt for finer needle and thread sizes.
• Reduce the stitch density (stitches per inch), thereby reducing the yarn displaced in the stitch line.
• A chain stitch or an over edge stitch will produce less structural jamming than a lock stitch.
• Avoid multiple rows of stitching which cause more pucker because the stresses in each row are cumulative.
• Use the finest thread size possible to assemble the panels prior to the topstitching operation when topstitching a seam.
Occurs due to: dimensional change in fabric and thread
Dimensional changes in thread or fabrics during post-sewing treatments or washing can cause pucker, primarily because threads and fabrics react to these processes differently.
For example, soft cotton threads increase in diameter and shorten in length when wet, as they absorb moisture. This can distort the fabric. Even though the thread may return to nearly original dimensions when dry, the fabric can remain puckered.
Test to identify
As such, there is no accurate scientific method to determine this type of pucker. However, a trained eye can find the pucker with a simple visual check – the pucker will appear on the garment after treatment/ finish or washing.
• The best way to avoid this kind of pucker is by using synthetic threads with low wet shrinkage properties. Also ensure that all components of the garment are compatible. For example, if a lining or reinforcing tape shrinks more than the base fabric, the base fabric will pucker along the stitch line.
• Similarly, if two pieces of material with different extensions are stretched during sewing, different relaxations can cause seam pucker on one face of the composite.
Occurs due to: poorly controlled fabric feed
When two plies of material are not fed uniformly, the variations are held captive by the stitches and cause feed pucker.
It generally occurs:
• If the foot pressure on the machine is too high, excessive friction can stretch the top ply. If the foot pressure is too low, the foot can bounce, momentarily losing control of both plies.
• When the operator stretches one ply more than the other as they are fed into the machine.
Many seams exhibit both conditions when the operator attempts to correct the unequal feeding of the fabric into the machine.
Test to identify
Make two cuts across the seam, and then remove all sewing threads between the cuts. If one ply is longer than the other, then the pucker has been caused by unequal feeding.
• Use a low friction presser foot.
• Adjust presser foot for optimum pressure, whilst still achieving positive and even feed of the fabric.
• Raise the back of the feed dog slightly to create a pulling effect away from the needle.
• Check the feed dog for correct height, teeth per inch, and number of rows of teeth which are appropriate for the particular fabric and operation.
• Make sure the operator is not holding back on either the top or bottom ply.
• Check for fabric hanging in any folders that may be in use.
• Match up feed and foot.
• The throat plate and presser foot should have needle holes approximately twice the size of the needle.
• If the machine has both top and bottom feeders, ensure that the timing is correct.
It is advisable to use threads with
• Finer sizes, with finer needles
• Sewing tension as low as possible
• Lower shrinkage properties
• Controlled elongation properties
Corespun threads and compact corespun threads closely match these requirements. With their high tenacity, they facilitate good sewing performance, which result in neat seams with a fine finish.
For pucker-free seams, Coats recommends
Epic Supermax poly-poly corespun thread
Epic poly-poly corespun thread