You will probably know the head to toe lycra or spandex bodysuits that have become popular at sporting or charity events and summer festivals. In the UK we tend to call them lycra suits whilst in the USA they are called spandex suits. The fabric is the same, majority polyester but with a small amount of lycra or spandex (or elastene) which gives the fabric a certain elasticity. This one piece suit is then zipped up at the back and covers the full body including hands, feet and face. The fabric is thin enough that the wearer can see out of course but the wearer becomes anonymous.
These suits originated in Japan where they are called zentai suits; the word zentai is believed to be a contraction of two Japanese words meaning something like full body stocking. Originally they were seen as suitable only for those with a lycra or bondage fetish but several brands in USA and Europe are now marketing these body suits as fun fancy dress costumes. The internet has enabled these costumes to be presented and marketed very cheaply with hi resolution images and social media to spread the word. The latest is Funskins! who suggest they may be suitable for stag nights and hen parties.
Lycra bodysuits are now produced in a huge range of fun colours and designs. In America they are sometimes called fan suits because they are produced in the colours of favourite Baseball or American Football teams. They are also ideal as super hero fancy dress costumes. In the UK there have been body suits produced in the colours of flags of the different nations and special body suit designs for Valentines Day, Halloween etc. These lycra onesie suits are clearly aimed at the youth or student market which is probably just as well as they tend to look better on slim, toned bodies.