That was Burt Rutan's particular gift to the state of the art.

A soft foam piece that was easy to develop into complex shapes,
and stayed in the part as a stiffening core.

Or remove the foam completely after layup, if it's not needed.

"Mold-less" construction.

Forgive me for jumping in to a forum to which I have no first-hand
experience other than supplying parts to you all who are building these
things.

I've been around the Rutan brothers since the vari-viggen and you are
correct. That was Rutan's gift to the art. And, there were a HELL of a lot
of Vari-EZ and Long-EZ aircraft made in what appeared to be a very short
time ... months, not years.

And when Rutan stopped supplying plans for those easy to build aircraft
somehow the time to construct took a quantum jump. Don't know why, just
observed the phenomenon.

Jim