Beryllium is old hat at this point, Yamaha has moved on from the NS1000 beryllium to the NS5000M and zylon now.
" The mystery material is a synthetic polymer called ‘Zylon’, which is manufactured in two varieties, Zylon-AS and Zylon-HM. It is used by NASA and in Formula One cars, and according to manufacturer Toyobo’s spec sheet for Zylon, it is indeed lighter and stronger than beryllium, its density 1.55g/cm3 compared with 1.8g/cm3 for beryllium, and its tensile strength 5.8 gigapascals compared with only 0.24 gigapascals for beryllium, and surpassing even carbon fibre at 3.5GPa. Zylon is also amazingly flame resistant, according to Toyobo, hopefully something prospective NS-5000 owners will never need to discover. "