Why do hems roll up?

Posted by Kathleen Fasanella on Jul 27, 2006 at 11:11 am / Process Reviews, Production, Quality, Sewing / Trackback

Susan asks:

Why is it that the small, double-folded hems common on jeans, denim shirts, and skirts roll up the way they do? It isn’t just denim, similar weight/feel fabrics do it too. Is there some construction technique or pattern modification that can eliminate this annoyance?

While I have my own ideas of how and why it happens, I went to the experts at American & Efird and spoke with Dan in technical support. I’m always happy to have an excuse to call them; they have a great reputation in working with smaller companies. Other than the most obvious problem which is related to laying out the goods improperly (patterns lain off grain) Dan explains the turn up is due to a combination of several factors. Some of these factors are:

  • Fabric properties: weave, finish and weight (exacerbated by the number of plies)

  • Seam formation: too many stitches per inch, excessive tension, seam shape (round vs longer and flat), thread weight
  • Operations: type of machine, type of folder or attachment and operator handling

Regarding fabric properties, the problem is due to sizing (seams are flat but turn up after washing) so you’ll have to test wash seam samples and correct other deficiencies to counteract fabric finishes if that is the problem. The most common reason is due to the properties of (usually) twill weaves most typically used in jeans. You can tell it’s a twill weave most easily from the wrong side, the threads run diagonally. If you can hem the goods counter to the weave, you can get better results.

Seam formation problems are usually related to too many stitches per inch, excessive thread tension or incorrect thread weight but again, there is no easy, pat answer. You’ll have to test wash samples varying these conditions to correct the problem. The problem is also more common in round, shorter seam lengths like jean hems. It is less common in longer seam runs which is related to handling problems in operations.

Operations related problems are often due to operator handling (dragging or pulling along the cut edge) and whether the folder or attachment is being used properly. Generally, if the fabric isn’t being fed neatly and fully into the folder, the hem can become torqued or “roped”. Roping is indicative of uneven feeding into the folder or even if the hem is turned by hand. If the hemmed edge is round rather than straight, roping is more common because the bottom of the hem edge is actually wider (longer) at the hem fold line than at the stitch line, causing the hem to flip up. The best way to correct this kind of defect, other than correcting folder usage (Dan describes those as “bulldog” hemmers) is to use a needle feed machine. I don’t have one of those; they’re a great solution to feeding tricky goods.

Thanks to Dan, I hope this answers most of your questions and I’d encourage anyone to consider buying from A&E; it’s a great company (one of the few companies I wish would advertise on my site). They sell a lot of components like zippers and such too. You can find the rep in your area at sales and service. Unfortunately, the drop down box on that page doesn’t work in my browser (I’m running Firefox) so if you have a similar problem accessing the right department, call headquarters from the home page (704-827-4311).

One Response to “Why do hems roll up?”

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anne
November 7th, 2006
9:36 PM

Could it also be because there’s all that extra weight on the back? Not to discount the other issues, but a hem on a pair of heavyweight jeans is a lot of thick layers of fabric in a relatively narrow area.

Knit fabric (single-knit jersey) rolls towards the knit side and away from the purl side because there’s more yarn on the purl side – all those wiggly bits (technical term – and the smooth knit side basically loses the tension fight. Knit designers get around that by adding purl stitches on the edges – ribbing or knit/purl patterns like seed/moss stitch. Surprisingly, you don’t need a 50/50 proportion of knit to purl stitches to stop the roll. I can’t remember the requirements, but it’s no more than three knit stitches to one purl, maybe less.

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