Pop Quiz: Why do knits get larger?

Reverse shrinkage means just what it sounds like. In wovens, reverse shrinkage is most often due to chemical properties of the fabric and if not dry cleaned, the weave will loosen from its previously crisp state and get billowy. Is billowy a word? This happens a lot with inexpensive rayons -as I would know from shopping the dollar a yard bins so it serves me right. Sure, you pay less for fabric but the pass along cost to the consumer is higher on account of maintenance.

Reverse shrinkage in knits is usually due to something else. We’ve all experienced it. You buy a shirt, skirt or slacks and after one washing, the garment is wider than before. Do you know why this is? Believe me, you don’t want to find out about reverse shrinkage the hard way when people start sending the stuff back. They can send it back because it’s a manufacturing defect, not a fabric flaw.

If you think you know the answer, let us know in comments. If you know the cause, you also know how to prevent it so be sure to explain that too. Thanks!

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16 comments

  1. anne says:

    I cannot comment on the washing; it used to be in that the “olden days” when knits were cut the plies were laid up and then allowed to “relax” before cutting. I am not sure how this impacts what you are talking about, but I know that this is not a common cutting practice anymore in the land of turn it around asap.

  2. I don’t have an answer to contribute, but I wanted to say this: I just tried searching online for the answer to the question, and like so many topics covered on this site, it was nowhere else online. A lot the information here might be considered obscure, but it’s very pertinent to me. So thank you for creating such a one-of-a-kind source! I’ll be waiting for the answer here :)

  3. kay says:

    Loops elongate lengthwise during knitting and wet finishing; when they get washed, the loops “round out” when they relax, becoming shorter and wider, so the fabric becomes shorter and wider.

    I believe that at least some “better knits” get run through sets of rollers during fabric finishing that act sort of like a differential feed on a serger, making them closer to the “after wash” dimensions. I think it’s called overfeeding, but I’m fishing in deep, dark memory for the word.

  4. dosfashionistas says:

    This is something new to me. I know about length shrinkage in knits if they are not allowed to relax before cutting. And there can also be shrinkage with washing due to chemical shrinkage as the finish is removed. But this is a new and different problem and I am delighted to learn about it.

    I love to learn new stuff. It just delights me that after being in the garment business since 1964 there are still new things to learn. (Actually it is more fun now that the learning does not involve an angry boss wanting to know how I could have overlooked the problem.)

  5. Ohh this one has sooooo many causes I don’t know where to start!

    Firstly Kay is absolutely correct that lengthwise shrinkage occurs and the fabric needs to allowed to relax so it widens and shortens … three cheers that somebody got the “widens” part in there. Lengthwise shrinkage is mostly due to the speed at which the fabric is spooled on to the roll. The company wants to spool as fast as possible but not stretch the fabric too much. The different weights of the fabric can be spooled at different speeds … the faster its spooled the less time there is for gravity to create say between rollers and so on. Usually 5% stretch is unavoidable when spooling. Thus you need to let the fabric relax on the table before cutting.

    Now if you’re an overly inquisative person like me you’ll actually measure the length on a cutting table the night before to see if relaxation has actually occured. Heres the catch … depending again on the weight of the fabric, the number of layers and the friction on the cutting table you rarely get relaxation at all … at least in the longer layups you don’t!

    OK but what about reverse shrinkage? The main one is usually when you get cheaper quality textiles running on old equipment … they don’t spool anywhere near fast enough so the knit loops aren’t fully extended and released in the earlier part of spooling (maybe what Kay is also mentioning). How do you fix it? Stretch your fabric before cutting and allow itr to relax in shorter layups … or buy a better quality fabric.

    The other one is where you have a low weight fabric that’s quite transluent because the fibre is small and the knit is course. These fabrics distort easily and don’t rebound well (talking synth/spandex here).

    Cheaper quality polyester or polyamide micro fibers also expand when warmed and don’t return to their original length on cooling. Simply sitting in the back of a delivery truck in the sun for a few hours can literall destroy a synthetic when under tension on a roll. You can tell it’s happened when you see puckers every few inches closer to the selvage and it takes stretching the roll to eleviate the puckers (ie; selvage length is different to center length) … you can save the roll only by allowing it to relax and discard the section on each selvage and the first 10 meters or so of the roll (any part that’s puckered after relaxing) – This happens way more than you think it does. Avoid cheap fabrics!

    Multistrand fibres (wool, cotton etc) get tense during knitting just like they do during weaving and slip and stretch for exactly the same reason.

    Lycra/Spandex fibres also have a certain amount of tension in them even when the fabric is relaxed. If the fibre is overstretched (eg; too fast spooling) it heats up and may not return to its original length … as the synthetic lengths are calculated into the equation as tensions you find you have loops that open up the very first time you take it off the roll … then you cut the garment and durring construction it stretches and distorts and doesn’t rebound to expected size. Again warm storage conditions can create this problem … as can many things really.

    There are many chemical treatments applied to synth/spandex knits but these are designed to stay on the fibre and not necessarily be washed off. Some help with fibre life, moisture wicking, dye absoption, fire retardance and a billion other reasons … see the carvico and jersey lomellina websites! They can make the fabric “tight” at first but with rolling and rerolling I find this isn’t an issue. I dislike retreating/washing fabrics for ready to wear … crisp sells better. Let the manufacturer do it and if its a problem find another manufacturer.

    Hints to avoid “reverse shrinkage”:
    – buy good quality textiles from someone who you know knows what they’re doing.
    – store your textiles in a cool dry place and always on the roll.
    – make sure your textiles are delivered in cool dry conditions.
    – allow your textile to relax before cutting and try shorter layup lengths (eg 2x4m layups on an 8m table for example.
    – check the rebound of the fabric corresponds to expectations (data specs from the factory or from your own tests)
    – measure relaxation on the table before cutting (not reverse shrinkage but still do it)
    – make sure sublimation printing is according to spec (heat is the enemy of a knit every time).

    Lastly it’s often hard to identify why reverse shrinkage has occured in a particular knit but it’s usually typical of a specific textile or a specific manufacturer … avoid them in favour of one that doesn’t. They’ll soon ask why and fix the issue!

  6. Barb Taylorr says:

    Wow, Stuart! Thanks so much for all this fascinating & helpful information. How exciting to have my eyes opened to reasons behind so many things I have observed over the years. Thanks Kathleen for asking the question! What a great way to start the day.

  7. THANK YOU, Stuart for your detailed response. I work with poly/spandex and have observed some of what you’re referring to and I figured I was the culprit somehow. Specifically, I cut something and when I sew it, lengths aren’t lining up and I swear I cut it straight. Now I’m going to give it time to relax before I cut and see what happens.

    Thanks, also, to Kathleen for asking this question.

    Marguerite

  8. Marcy Tilton says:

    I will double the WOW on this info, had a big aha as I read Stuart’s post. I work with the home sewing community. In our world, we pre-shrink knits, toss them in the washer/drier and then touch up press, then cut and sew….so that takes care of some of the issues you discuss, and explains others. The knit that consistently displays reverse shrinkage is cotton interlock, which is one of the fabrics I avoid like the plague. It stretches crosswise while working on it and seems to continue to grow in wearing. I’ve attributed it to 1) no lycra/spandex so there is no recovery and 2) cheap short fibers, but now see that the very construction and other conditions contribute too.

    In addition to teaching, I have an online retail fabric business, buy fabric from jobbers and have seen some of the problems discussed here in the fabric that comes in……some, I suspect, might be offloaded from manufacturers who had these kinds of issues in their cutting rooms.

    Great question, Kathleen. I love learning —- this falls into the category of those mysteries I didn’t know I didn’t know, and a big lightbulb just went on! I seek out knits, love working with them, but every so often there is a ‘bad seed’ fabric that shows up, now I have a better understanding of how the manufacturing and even storage can impact the fabric.
    Marcy

  9. Theresa in Tucson says:

    Marcy, thank you for the tip on cotton interlock. I’m just beginning to sew with knits so it’s nice to have guidance from someone who knows. I think I will leave the cotton interlock alone or buy it RTW.

  10. sahara says:

    As a designer and knitter, I can offer this explanation for wool. The fiber, like our hair, has scales which interlock with each other upon washing and with time (felting). This also depends the amount of washing or dry-cleaning, etc. or the type of fiber itself; some breeds of wool are more resistant to felting.

    Fiber mills, in order to render the yarn easier to launder, will either coat the scales with a plastic resin (gluing them), or will chemically remove the scales altogether (which weakens the fiber and causes you to get that hole in the elbow of your blazer faster).

    The result of this “superwashing” of wool, is it grows. @##$^! Worse is clothing labels won’t necessarily say that the cloth is “superwash wool”.

    This is why when shopping for wool cloth, I’ll buy only a yard or so and delicate wash one half and have the other dry-cleaned, then compare.

  11. mary allen says:

    I cannot thank you all enough for this insightful question and answer. The rubber band analogy was the best. Thank you Katherine for posting the quiz and picking our brains….and Stuart for the answers to questions I did not know I needed. Happy Spring everyone….

  12. Marie-Christine says:

    A heavy knit can also grow lengthwise, especially if it’s cotton. A friend of mine had a really dramatic example in a handmade lacy cotton cardigan. The friend is large, there were at least 2lb of cotton in there, the garment went from cardigan in the morning to dress at noon and finally a train at night, it had to be washed and machine-dried every single time it was worn :-(.

  13. Johanna Lu says:

    Thank you so much for this posts. I had this happen with a non lycra cotton/rayon rib knit lately that I cut straight from the roll and it grew widthwise like no tomorrow. It has the same properties as cotton interlock that Marcy mentions above and I was so disappointed. I had originally planned to use the fabric for my small clothes line, and was just testing it for a personal project, but since I can’t guarantee the shape of the garment, it will keep it just for my own use. Though I reused the pieces after the first failed attempt, and then the fabric clearly had enough time to relax so it worked much better, but still not good enough for qualifying itself into commercial use. And the fabric is from a very reliable high quality local factory that I have bought from several times in the past.

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