A number of metals have been tried and the heavier metals have found favour. In particular stoppers & crowns made of FLUTEMET have found favour with professional players. See Products page for what is available.
However a user of my piccolo stopper and crown made of aluminium- a light metal- had this to say:_
"today I received the stopper and crowns and I have to say that I was astonished when I tried them! I noticed a huge difference in tone quality, intonation- especially in the high octave!!!, and it is sooo [sic] much easier to play it is much more responsive... "
DAVID SYMINGTON- FLUTE AND PICCOLO STOPPERS AND CROWNS