TRABEM writes:


Are metalized polyester caps just as good as metalized polypropylene
caps?

Mylar caps are pretty good, but not as stable or as high @ as polystyrene.


Wrap-and-fill polypropylene are a lot better than metalized polyester (mylar
is a trade name for polyester). Mylar also absorbs water and shifts its
Q with time rather badly.

If you care about Q for large values, polypropylene is going to be your
best shot. There are other caps (teflon, and other exotic materials) that
are better, but you also seemed concerned with cost. Higher voltage for the
same value with give a better Q.

Good luck.

Steve.
--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA