The combination of close-to-feather shuttlecock flight performance and four to five times more durability than an ordinary nylon shuttlecock makes the YONEX MAVIS series the most cost-effective choice for practice sessions The hardness of the skirt ? the feather part of the nylon shuttlecock ? varies depending on temperature. ? Natural Cork ? Green Cap Slow/22?C~33?C ? Blue Cap Medium/12?C~23?C ? Red Cap Fast/0?C~13?C.