Before the start of each season, ski jumpers are measured using 3D body scanners, in which they must wear only “elastic, body-tight underwear”.
Rules state their suits must have a tolerance of only 2-4cm, and as part of the measuring process, their crotch height is also measured.
The crotch height of their suit must conform to the athlete’s crotch height, with the addition of 3cm for men.
Hyularonic acid injected into the penis can last up to 18 months.
There have been previous attempts to improve performance through manipulations of the suits.
In August, Norwegian Olympic medallists Marius Lindvik and Johann Andre Forfang accepted three-month suspensions for their part in the tampering of suits during the men’s large hill event at the World Ski Championships in Trondheim, Norway, in March.
While it later transpired the athletes themselves were not aware of the tampering, FIS said their team had “tried to cheat the system” by putting reinforced thread in their jumpsuits.
Both athletes are set to compete at these Winter Olympics, which officially start on Friday.
The men’s ski jumping competition begins on Monday.
BBC Sport has contacted FIS for comment.