Pop Quiz: Does fiber content affect fabric weight?

Another Karen (not the same as yesterday) writes:

My company supplies an item with an agreed spec of 90% poly/10% cotton. A random test showed the item weighed significantly less which caused a huge problem. I realize there are a lot of variables that go into the weight of a fabric, but I am the only person at my company who believes fiber content has something to do with the fluctuation. Am I wrong? It seems very logical to me that a decrease in cotton is what caused the test to fail and substituting a new fabric at 82/18 will weigh more because there is 8% more cotton. Controlling the weight means controlling the fiber content. Am I wrong? Why does everyone keep telling me material breakdown and weight have no correlation?

I think you know what to do.  Leave your responses as to whether fiber content affects fabric weight and why or why not in comments. We’ll be giving away a prize to the first most complete answer; a copy of Patternmaking in Practice donated by Lisa Bloodgood. Good luck everyone!

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19 comments

  1. D says:

    Karen doesn’t say what the “item” is. Whilst polyester is known for its lightweight qualities compared to cotton, the purpose of the fabric (eg sailcloth, summer dresses, hard wearing work clothes, belts) would affect the finished weight, since each type of fabric is woven differently, using variations in yarn, weave, thread count, crimping, thickness etc to enhance different desirable properties (such as strength compared to softness, durability compared to lightweight). All these factors can affect the finished weight of a fabric, as well as the composition, in this case a polyester/cotton blend. Adding more cotton may up the weight, but not if other properties are changed in the process and again this will depend on the weight of the cotton yarn added, its density, as well as the method used to weave it into the cloth.

  2. WLS says:

    Of course fiber content affects fabric weight as different fibers have different specific weights. So you have to specify both fiber content as well as fabric weight when ordering fabric. For instance you can order 100% cotton denim in (standard) weights of 12, 14 or 16oz. Make the same fabric in for instance a polyester/cotton mix, and you will end up with a different fabric weight.

  3. Lesley Miller says:

    I would say no. I can order a fabric with the same fibre content in two seperate weights (for example – a cotton/bamboo/spandex in 70/20/10 content, in a 220 gsm and 280gsm). They have the same feel and memory, but the heavier weight feels.. .well, heavier.
    I would say that it has to do with the thickness of the yarn that they knit with in stretch, kind of like how a bulky yarn when you are knitting by hand will result in a heavier weight finished garment.

  4. sfriedberg says:

    Karen is right, but so is everyone else at her company. Fibre composition does affect weight, but it’s a minor factor compared to other things.

    Keeping all other factors unchanged, changing from 90/10 to 80/20 poly/cotton will only increase the fabric weight by one percent.
    Polyester specific gravity 1.28
    Cotton specific gravity 1.54
    .9*1.38 + .1*1.54 = 1.396
    .8*1.38 + .2*1.54 = 1.412
    1.412/1.396 = 1.011
    Actually — again keeping all other factors unchanged — a 100% cotton fabric is only twelve percent heavier than a 100% polyester fabric. So changing the poly/cotton proportion can’t have a bigger effect than that.
    1.54/1.38 = 1.116

    On the other hand, increasing the yarn size or the ends-per-inch by 10% (holding all other factors unchanged) will increase the fabric weight by ten percent.

    So it’s not that there is no correlation between material breakdown and weight; the correlation is simply small. Or stated differently, controlling the fiber content in isolation is completely insufficient to control fabric weight.

  5. Sarah_H. says:

    I am going to answer before I read any answers, since I am sure someone with more knowledge has made a through answer by now. I say Yes, the fiber content will influence the weight of the goods, and no, the weight difference will not necessarily be due to the fiber content. First, different fibers have to have different weights. If you could have the same denier and the same length of each fiber, it would show a difference in weight. However, fiber comes in many deniers(a measure of the thickness of a strand), and may be tightly or loosely twisted, and these things also will influence the weight of the goods. I could not tell you the comparative weight of polyester and cotton, but if the product is supposed to be a 90% poly/10% cotton and have a certain weight, you will solve your problem by finding a thicker fabric, not a different blend.

  6. Dia in MA says:

    I’m assuming the contract specifies the 90/10 proportions. Changing that requires new negotiations with the customer. There are a lot of other factors that could be affecting the outcome that should be checked first. 90/10 is a proportion so the weight should not be changing this way. If there’s been a change, the source needs to be found to avoid repeating the problem.

    As D points out, synthetics like polyester can very hugely. Not only the thickness of the yarn, but how the fiber is created. Hollow fibers and assorted shapes of fibers with different properties can all make a difference. Two fabrics with the same fiber proportions can have very different characteristics. There are a lot of factors involved here. Is it possible that the type of polyester fiber has been changed? If a new provider is being used this could have changed.

    If a different type of polyester fiber is being used, the fabric could have the 90/10 proportions but be very different. Changing the proportions might not bring back the original characteristics if this is the case.

  7. Teijo says:

    If the fabric’s fibre ratio is specified at 90% polyester and 10% cotton, it means that the ratio of polyester to cotton must always stay nine to one regardless of the fabric weight. Thus in this case the weight cannot be adjusted/controlled by changing the polyester/cotton ratio.

    Given just the weight (let’s say 100 g /m2) and fibre ratio (90% polyester / 10% cotton) specifications, we know that more raw material must be used per square meter. If in this example the fabric is 90 g/m2, to bring it to the specified weight while maintaining the specified fibre ratio we would have to add 9 g of polyester and 1 g of cotton per square meter.

    Off hand, fabric weight is affected by thread weight and thickness, fibre ratio, and weave/knit density, thickness and pattern. Since changing the fibre ratio is verboten and changing the weave/knit pattern would result in a different fabric, it would seem we’d have to play with the remaining parameters, or thread weight/thickness and weave/knit density and thickness…

  8. Brenda says:

    In addition to the items that have been mentioned, I wonder about the quality of the fibers. For example, a short staple cotton is not going to be as strong as a long staple cotton, right?

  9. paula says:

    I agree with Karen. Polyester is a lighter weight fiber than cotton. Although this is a somewhat separate issue, the thread count also will affect the fabric weight. If you want to decrease the amont of the cotton fiber content, I would think that the thread count would need to be higher so that the fabric weight would increase.
    Does the spec need to comply solely with the fiber weight or is the resulting fabric weight taken into consideration?

  10. If the fabric is 100 g/m2, it will be 100 g/m2 no matter what the fibre composition is. It could be spider silk, it is still 100 g/m2.

    How is the fabric being specified? If the agreed spec is 90% poly/10% cotton, presumably not just any weight is acceptable. That spec could apply to a gauzy fabric as well as canvas or upholstery weight. Is there a weight spec in addition to the composition spec?

  11. Sabine says:

    I very much agree with Sarah’s comment. I know that 5 meters of 8 oz hemp are thinner then 5 meters of 8oz cotton.
    So it stands to reason that if the fabric thickness and density stayed the same while the weight alone changed, that fiber content plays a role.
    That does not mean the fabric in question has changed fiber content, I assume it is simply thinner, therefore lighter.

    does different weight make a difference?
    Depends, if you have woven fiber, then you buy x amount of length of x weight fabric, the “only” two things change will be the the cost of shipping, as it is weight dependent, and any areas of your pattern where you needed to consider the fabric thickness. Besides the fact that a different weight fabric will make everything hang differently etc.
    On knitted fabric it can be a big deal, as it generally gets sold by weight, not by meter. If you buy 500 pounds of knit fabric expecting to get 350 meters out of it but instead you only get 300 meters out of it, that is a very big deal.

  12. Quincunx says:

    I was going to be flippant and say “if there wasn’t a weight spec, why were they weighing it?” but maybe it WAS being weighed for some non quality-control reason, or the freight quote came in at an attractive low rate and someone inquired into getting more of those better rates.

    If there is no perceivable difference between the fabrics, were the initial or the problematic weights taken in a time of extreme humidity? 10% cotton is still enough cotton to get saturated and weigh more than identical 90/10 fabric in a dry spell. Even 100% polyester garments can be weighed down by water even if they can’t absorb it.

  13. Paul says:

    This can be very simple or very complex (as in technical), with the same result, so I’ll start with simple. Something obviously changed from the initial condition to the lower weight condition, so let’s use the process of elimination to ferret out the culprit.

    Karen only identifies a change in fabric content ratio, so if we assume the exact same polyester and cotton fibers were spun in exactly the same way to create a fabric of the same thickness and thread count or density of weave, with only the content ratio changing, then the change in weight would be proportional to the difference in ‘average’ density of the two materials. I don’t know what those are for cotton and poly, but I would guess they are not identical. If that is true, then yes, the items would weigh the same, (assuming they are all cut and fabricated as identically as people are capable of, and the conditions under which they are weighed – such as using the same calibrated scale, and were stored in the same environmental conditions prior to weighing so their moisture content is identical). It’s physics. “Gravity, it’s not just a good idea, it’s the law.” Change one of those things I am assuming are the same, and you will introduce other factors that could balance out or ‘outweigh’ the density of the basic fiber. And when I say density, I mean the actual density of the raw fiber (kg/cubic meter), less all the ‘fluff’ created by the air around it.

    So it’s clear there are a whole host of other factors which will impact the weight. But Karen didn’t say why the change in weight (less) was a “huge problem.” Certainly not for shipping costs. Could it be customer perception? If the fabric feels and behaves the same, i.e. thickness, drape, etc, then I would really like to know why heavier is better. Is the customer paying by the pound?

    Can’t wait to find out more.

  14. Clara Rico says:

    Just a question: How is the 90/10 difference determined? Is it by weight or by volume? I thought it was 90% of the weight was polyester and 10% was cotton. Changing the proportions will affect the characteristics of the fabric but not the total weight. (The total weight is 100%.)

    To get the right temperature of bathwater, you need the correct proportions of cold and hot water. If you endup with too much water, changing the proportions will only give you too much water that is also too hot (or too cold). Change the amounts of both, keeping the proportions constant, and you should get what you want.

  15. Amanda says:

    Sorry, I’m no expert here, but weighed less than what? The spec given is fiber content, and variation in fiber content will affect the weight of the garment, but are you saying that the 90/10 goods weighed less than you agreed that your 90/10 goods should weigh, and so you suspect that the contents were not 90/10? Or are you saying that you changed your spec from 90/10 to 82/18 and didn’t change anything else, and you observe a weight change that you didn’t expect, but that you attribute to a difference in fiber content?

    The weight of the goods and the fiber content should be independent variables. You should be able to make a 90/10 fabric that weighs 100g, or an 82/18 fabric that weighs 100g. The dependent variables would be the thread weight or density, given these two specs.

    I am probably missing something….

  16. Paul says:

    In the middle of my ramble I said ‘yes, the items would weigh the same’ but meant to say they would not weigh the same (due to the fiber content difference).

  17. Kelly says:

    The reason material break down and weight have no correlation is because when you have a percent it is describing what “part” of the “whole” is. Not the weight or mass of the object.
    It is not fiber content, but fiber “density” that has to do with the fluctuation. I think it comes down to the weight of each fiber/thread used. Because if you started with a more densely twisted thread you could still have the same threads per inch. This would cause your fabric to weigh more, but you would still be able to attain the same 90/10 percentage.

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