FINA (Fédération Internationale de Natation) is the regulating body whose rules apply to international and Olympic events.
From their General rules: http://www.fina.org/project/index.php?option=com_content&task=view&id=43&Itemid=119
"GR 5 SWIMWEAR
GR 5.1 The swimwear (swimsuit, cap and goggles) of all competitors shall be in good moral taste and suitable for the individual sports disciplines and not to carry any symbol which may be considered offensive.
GR 5.2 All swimsuits shall be non transparent.
GR 5.3 In swimming competitions the competitor must wear swimsuit in one or two pieces which shall not extend beyond the ankles, the wrists and the neck. No additional items, like arm bands or leg bands shall be regarded as parts of a swimsuit.
GR 5.4 The referee of a competition has the authority to exclude any competitor whose swimwear or body symbols do not comply with this Rule.
GR 5.5 Before any swimwear of new design, construction or material is used in competition, the manufacturer of such swimwear must submit the swimwear to FINA and obtain approval of FINA.
FINA Requirements for swimwear approvalImage
GR 5.6 The manufacturers must ensure that the approved new swimwear will be available for all competitors. "
From FINA Requirements for swimwear approval: http://www.fina.org/project/docs/rules/REQUIREMENTS%20FOR%20SWIMWEAR%20APPROVAL.pdf
"3. CRITERIA
3.1 Swimsuits
The following criteria will apply:
(a) Design
• Decency: the wearing of the swimsuit shall not offend good moral and
taste (in particular but not exclusively because of the cut and of the
parts of body, covered or not)
• Surface covered: the swimsuit shall not cover the hands from the
wrist, the feet from the ankles, the head from the neck. Limits at the
wrists, ankles and neck are shown in exhibit1.
• Composition: swimsuits must be in one piece for men. They can be in
two pieces for women, one covering the upper part of the body and
one the lower part. Other items covering the body and not part of the
swimsuit are prohibited.
FINA Requirements for Swimwear Approval (FRSA) - 21.11.07
FINA, Avenue de l'Avant-Poste 4, CH-1005 LAUSANNE
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(b) Material
• Health. The material used shall not put the health of the athletes at
stake.
Regular flat fabrics and exclusion of outside applications: the fabrics
used shall be regular and shall not form outstanding shapes or
structures, such as scales. No outside application shall be added on
the fabrics (use of different fabrics, see below). For the avoidance of
doubt, impregnation is not subject to limitation and paint can be used
for motives in regular and usual thickness. It is further clarified that:
the application of fabrics put on top of each other as a result of a
manufacturing/application process to combine the fabrics is
permitted provided that this remains in the usual thickness and
does not create outstanding shape(s) or structure(s).
• Variety of fabrics: Different fabrics can be used in one swimsuit.
• Colours: for the avoidance of doubt, colours shall not be considered
as part of the design for the purpose of these provisions
Construction
• Seams shall be functional and shall not create outside shapes.
• Laces: are permitted to hold the swimsuit around the waist."
EDIT: HOW did that smiley appear?! EDIT 2 : It is because the "c" point (Construction) is written ( c ) which creates a smiley if you remove the spaces between the parenthesis. The official FINA document does not contain Smileys.
