From the specs (390 gram!) and the fact that it seems to appear on frames from
$1200 upto >$3000 and that cheaper bikes have aluminum forks, it would have to
be primarily carbon, possibly with carbon steerer in the higher altitudes and al or
steel steerer in lower price models. Oddly steel doesn't add a lot of weight to the
fork, presumably because this is an area where engineering safety rules. If you
want a lite fork you go to carbon steerer. Steve