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How To Fathom Flotation With A Valid Test

Feb 19, 2009  - Craig Lord

Suit Week Sequel – Part 4: In our final article on suits before the meeting in Lausanne tomorrow of suit makers, coaches, swimmers and others, we consider the one thing that must be a part of any new, professional framework that carries the confidence of the sport: a valid test for flotation

In a sport dominated by stats and numbers, one more set governing a test for flotation of suits on humans should not be too cumbersome for the sport  of swimming to stomach. 

Having talked to Milt Nelms about his work with swimmers and having identified flotation as the single overriding factor in the fast-forward pace of progress on the clock in 2008, it seemed reasonable to ask him how the sport could hope to test for flotation.

Below, in original form, with nothing added (expect explanatory links in square brackets) or taken away, is the informative and instructive reply from Nelms:


By Milt Nelms

The following should be read alongside this illustrative sketch

Flotation is in the realm of simple common sense, almost outside the realm of science. The physics of flotation are among our most familiar experiences and images. All of us know what boats look (and feel) like. We have been in the water ourselves, and felt our own flotation, and the flotation in balls, tubes, foam, and rubber ducks. Many of us have played with kickboards, and immersed glasses, right side up, in dishwater and felt and watched them fill with water and sink. We have an intuitive and familiar grasp with the concept of floating and sinking. However, to certify fairness and compliance with rules, the testing of flotation should be rigorously scientific.

Buoyancy in a swimsuit is performance enhancing, so, according to the rules, a swimsuit cannot make a person float [according to Rule SW10.7].

Flotation testing needs to be done to find out two things:  

  • 1. Does a suit on the body have flotation that lifts the body higher in the water? Refer to Sketch 1- Body buoyancy
  • 2. Does a suit on the body have flotation that lifts the legs towards the surface? Refer to Sketch 2-Leg buoyancy

There is another way to say this:

When a person puts on the swimsuit, their Aquatic Signature cannot change for swimming advantage. To avoid making a swimsuit that helps a swimmer go faster, there need to be tests to determine that this change in the Aquatic Signature does not happen when the suit is put on.

Flotation/buoyancy testing methods

If you put a swimsuit in the water on it’s own, and it floats or sinks, it does not mean that it will act the same way if stretched over a human body. 

Flotation testing of a suit off the body will not work. Using real human beings as part of the method of testing can be done with accuracy. However, the number of variables and difficulties with repeatability make using real humans scientifically problematic, so using real humans for testing will not work either.

The solution is to use a device that will mimic the relevant traits of an actual human being in the Aquatic Signature.

Textiles and flotation

Fibers and textiles tend to have one of two different characteristics. They tend to be either hydrophilic (Hydro for water and philic for love), or hydrophobic (Hydro for water and phobic for fear, or fearful).

Fibers in a hydrophobic textile have a tendency to repel water and float. Textiles made from hydrophilic fibers tend to absorb water and either sink or become buoyant-neutral. There are many variations on this theme, but in a general way this describes textiles and the water. 

An example of a hydrophilic textile would be a cotton T-shirt. If you throw the shirt into a tub of water the fibers will saturate and the shirt will sink. While natural fibers tend to sink, some woolen clothes will float.  Modern synthetic fibers, such as nylon, are often, but not always, hydrophobic. Hydrophobia or hydrophilia in the fibers can be introduced during the manufacturing process in many ways. 

The fabric of a rubber raft is very hydrophobic, as is the fabric in old-fashioned logging coats that are made of wax-coated canvas. Gore-tex clothes and shoes are hydrophobic, but the fabric is manufactured as a membrane that will allow the moisture in perspiration to pass through in one direction, but stop rain from penetrating from another direction. Modern engineering and design are capable of doing remarkable things with fabrics.

Fibers and textiles have two variations in the hydrophilic-hydrophobic relationship: 

  • They can be anywhere on a gradient between very hydrophilic and very hydrophobic, so they can be “somewhat” water repellent or “somewhat” water absorbent.
  • They can also change with conditions-duration of immersion, water temperature, fresh or salt-water, agitation, etc.


The reason that testing “off the body” will not work is that a suit may sink when it is off the body, but may become buoyant when it is “on the body”. One way that change from non-floating to floating can be caused is by the sealing of air into the fibers or the weave or knit of the textile when it is stretched, which would add flotation. Also, as many swimmers are reporting, air can get trapped between the skin and the suit, which can also add flotation. Some suits are very good at holding air all over the entire body, which could be different on a firm surface. 

However, using real human beings also presents obstacles. A repeatable and accurate Aquatic Signature is a learned skill. A number of variables can change the quality and appearance of the Signature. Repeatability and limited variables are what make the results of a scientific test valid.

Many of these variables are subtle and difficult to manage. Things like slight tension in the tissues, a slight change in the angle of a joint that repositions a limb, or the amount of air in the lungs can make huge differences in the apparent angle of the Signature, creating misleading impressions. Observation and analysis of the signature is a learned skill. A population of testers and observers would need to be trained, much in the way that wine tasters or coffee tasters develop their skills. All of these issues combined make the use of humans as testing subjects for flotation in swimsuits problematic.

The solution is a test that mimics the traits of the human body, while the body is in the Aquatic Signature.  Such a test requires a device that will imitate the human body in the Aquatic Signature at zero buoyancy, a device which needs to mimic two traits: texture and form. 

The device needs to stretch the suit as it would be stretched on the human body, and the texture needs to be gelatinous, in a quality similar to the body.  A solid form will not provide complete information about the textile’s response to human tissue, because engineering and design can provide suits that could have one flotation response to human tissue and a different response to firm or hard materials.

The testing device needs to be in a form, or shape, that will test for general upward flotation (vertical buoyancy), but also the distribution of flotation. Suits can be engineered to sink in the chest, but float in the legs. One test might show that, overall, the suit does not float. However, flotation could be “hidden” in the legs. A test needs to be able to tell if this is happening, because flotation in the legs can aid performance, as was described here [LINK previous article]. 

After reading the above, SwimNews asked Nelms the following questions:

Q: Where would swimming look to find independent people or companies capable of carrying out the necessary tests?

A: In my opinion, industrial rigor should be used to develop the testing and the equipment used for testing, rather than academic or sport science resources. In other words, the tests should be designed and done by people who normally need to do tests rapidly and with importance (beyond sport performance) attached to the accuracy of the outcomes. 

Q: When you say industrial rigour, what do you mean?

A: It should be as though an inaccurate test would result in the loss of millions of dollars or the loss of life. 

Q: In general, what should any testing regime be aiming at?

A: It should establish overall buoyancy; distribution of buoyancy; create unique and reliable testing devices; create repeatable methods; create quick turnaround.

FINA has stated its commitment to solving the problem - and there is no reason to doubt that. Indeed, there is reason to believe that the international federation has been looking in the right direction. Flotation is not the only problem (there's biofeedback and mechanics and suit shapes) but it is the base block to all other issues. Tomorrow will deliver, if not the final decision, a strong hint as to what kind of sport swimming is to be in future.