The objective of stretch fit patternmaking for swimwear is to create a pattern which will result in a garment of even (not necessarily equal) tension on the body in all directions. This is critical. If tensions are not even then the garment will ripple and move on the body. If you think of a one piece swimsuit as a tube that encircles the body there are two questions to consider. How long is the tube and what is its circumference? These are the two principle stretch directions.
To make a swimsuit ‘shrink’ onto the body at least one of these directions requires what is referred to as negative ease. Negative ease is where a body measurement is reduced by a certain amount in the pattern. It is the opposite principle to adding ease to a measurement for non-stretch pattern making. Generally, we reduce only the measurements that go around the body. There are two main reasons. Firstly, when a person twists and bends they do not significantly change any of their girth measurements, however they do change their body length. Thus adding limited or no negative ease in this direction adds a certain amount of softness to the garment when the wearer moves. If the garment is unable to stretch vertically, because it has already been reduced, it will move on the body rather than change shape with it.
Secondly, though more a consideration for ready to wear manufacturing, it is best to allow for more variation in girth than height. Clearly, you’ll fit more customers within each size if you set your principle stretch direction around the body. Try to consider each size as a range of measurements. For example, while we define a size 10 as an 84cm bust line, we would hopefully design a garment that would comfortably fit a bust of between 82 and 86cm, with similar allowance made for waist and hips.
Tip The more horizontal negative ease you include in your block, the smaller the number of people your garments will fit within each size. Can you answer why surf style swimwear brands fit just about anyone, while high fashion swimwear usually does not yet still sits a lot better?
There is also a subtle third reason which is complex and often overlooked. Put simply, when you apply tension to a stretch fabric it will naturally tend to shrink in a right angled direction. The fabric is trying to relieve the tension you’ve applied to it. How much it counteracts depends on the fabric. Recent fabrics with higher elastane content do not counteract as much, some remarkably not at all. You will need to test your fabric and make allowance for this amount.
Tip Sometimes the fabric will decide the direction for you. A single direction stretch fabric might have a print running only one direction, for example. Another might stretch more in one direction than another. Usually the fabric’s greatest stretch direction should run around the body.
The table below illustrates the typical relationship between horizontal and vertical negative ease. Generally the more you reduce the horizontal, the less you need to reduce the vertical to apply the same even tension to the body. Which set is used depends on the designer and the garment’s intended purpose.
| Negative Ease Direction | ||
|---|---|---|
| Horizontal | Vertical | Purpose |
| 8% | 4% | Dancewear |
| 9% | 3% | General Surfwear |
| 10% | 2% | |
| 12% | 0-2% | High Fashion Swimwear |
| 15% | 0% | |
| General relationship between horizontal and vertical negative ease for 180gsm, 75% two-way stretch nylon elastane. Note: this table was updated 1/2/2008 in light of newer fabric technology. |
||
Anyone designing swimwear needs to understand this principle almost second nature or they will forever be chasing themselves around in circles trying to work out why a particular garment keeps failing to properly fit or moves where it shouldn’t.
But how do you determine what total amount of negative ease is appropriate for any particular fabric the first time? You need to asses the fabric’s stretch and rebound properties. In the past many designers have simply wrapped a section of fabric around the bust until the tension ‘feels about right’, measured how much fabric was required at that tension and then compared it to the bust. For example, if it takes 74cm of fabric to comfortably wrap a bust of 84cm, you have a reduction of 74/84 x 100 = 88% or a negative ease of 12%.
These days manufacturers provide you with fabric performance statistics on request. They are required to perform national standards testing on all fabrics they sell. Which standard they use depends on the country and the measurement system used. This data should be able to tell you how much percentage reduction is required to create a certain tension. Some people still find this data difficult to interpret and resort to the old way of assessing a fabric, but I strongly recommend getting the manufacturer’s sales representative to explain how to interpret the system they’ve used as it will give you much more reliable and consistent results and save time in the long run.
For demonstration purposes this site will base all patterns on 12% horizontal negative ease and 0% vertical negative ease. These values suit the common 75% two way stretch swimwear fabrics. If you are making swimwear for the first time you might want to base your patterns on 10% horizontal negative ease and 3% vertical negative ease instead as this creates a more forgiving pattern.
Remember, every time you change your fabric, you may need to change your block, or the patterns you cut from them will not fit as nicely.
I’m sorry, I guess I should elaborate. Is it possible to take two-way fabric and create, say, a catsuit in which the wearer could bend down and touch her toes? It seems like there’s no way so much extra length can come out of a fabric allowing no vertical stretch. I did notice some relevant comments in your wetsuit post, but that’s not enough, is it?
Hi Stuart, do you see any role for two-way (not four-way) stretch fabric? Is there any way to make a decent stretch garment out of it? Here you talk about having different horizontal and vertical ease, even down to 0%, but you still rely on there being some stretch in both directions, right? Thanks!
Hi, I was browsing and found this site. I have an invention for infants and children who have feeding tubes. The garments are going to be made out of Lycra because the garments need to fit close to the body. Can you tell me how to take an “all around” measurement of the torso. This will be similar to a onesie with a pocket to hold feeding tubes. The old way was to measure from the hollow at the throat, down thru the crotch then up the back and over the shoulder to the approximate starting point. I am in the USA and we still use inches and feet and I’m too old to change.LOL
I was also interested in your “negative ease”. I’m making some custom garments for a few babies to test the product before finding a manufacturer…and until I read your info, I thought I knew what I was doing. Anything you can assist me with would be welcome and hopefully I will get this project in memory of my baby grandson off the ground before I croak!!! Sincerely, Kate Boyles
Hi Mikki, yes it is and no it isn’t … it depends on how narrow the thinner sections are. If there’s no section smaller than say 40-50 mm then it may well be a simple matter of cutting away the bits you don’t want. If you expect the solid side to be held back by a narrow strap however you’re likely to be disappointed … the narrower the strap, the more it stretches so you may need to shorten it a bit to keep things where they’re supposed to be. Now onto the actual cutouts … they are not going to curve in exactly the same way as the line on your pattern piece … a solid side obviously has more tension than one with several chunks missing … this type of garment is going to be a balancing act.
Technically you can calculate where the tensions are going to go (tension mapping) but with practice over the years I can simply “see it” and automatically account for it. I’m not sure I want to get into the mathematics of tension mapping (it’s really just vector analysis) because it’s probably a lot faster for you to just make a couple and tweak till you get them right by starting with leggings and doing cutaways … just keep in mind the paragraph above!
hi Stuart – i was asked by someone if i could do similar to this – it can’t be as simple as taking sections out of a leggings pattern can it? what about how the stretch direction is affected?
Thank you Stuart. The design has a high back so the centre back seam so I’m looking forward to trying out your suggestion above. The fabric I am using is a holographic lycra (shattered glass pattern?), the only information I have is it’s 190gsm and a 80/20 blend. Unfortunately retail shops don’t seem to have the information to give you about the stretch and rebound properties so I am having to guess using your method above. Thank you again for your assistance
Hi Kirsty … you could use the leotard block … same theory as my previous message. If you really want a true higher legline then try using a centerback seam to begin with and maybe increase the width more suddenly to the rear of the crotch line (takes a bit of practice and tweaking but when you draw it on the pattern it should make sense as to what you are seeing) … I wouldn’t necessarily do this to ordinary swimwear but with a center back seam on a one piece it’d just feel better to girls who are used to tanksuits. I might ease up on the tension around the waist just slightly (over and above the already reduced horizontal negative ease) and I’d probably lighten up on my elastic tension on the vertical by about 1.5% (just trying to avoid things locking at full stretch … when synchro garments seem to move!).
Kirtsy, for synchro I’d be looking at a lower leg line (for obvious reasons … even if there was a little skin tone section with the illusion of a higher legline) and probably 8-10% horizontal and 2% vertical (for something like carvico 384) … difficult to say without seeing your fabric ie; slightly less than max on the horizontal and add a touch to the vertical for all those backward somersaults!
Sorry me again, should I use the leotard block as the base or the one piece? (finally found where I had read you mentioned sync swimming, your search function is a wonderful addition to the site) And generally the leg is quite high cut, you mentioned there are ways of getting it to stay in place, how do you achieve this? Thanks again
Hi Stuart, just wondering what you would recommend for negative ease (I love that saying, it helped things finally click
yay), sorry back to what I want to ask. I am looking at making a swimsuit for a synchronized swimming costume what would you recommend as the horizontal and vertical negative ease? Thank you 
Please, consider putting a metric to US conversion chart on the right margin for we fools who live in the United States. I would have, gladly, gone metric, but I was too young to vote at the time.