I have used ceramics in place of paper caps with no troubles, but I also was careful how I placed them under the chassis.
The propelenes are smaller than polyester(mylar), and both have a "self healing property". In most of the radio reciever applications, you can use the cheapest cost as replacements without worry. Most "bypass" caps are just a smaller capacity with a slightly higher voltage rating, and insome cases better RF insulating ability.
Foil is just that,, and metalized film means that a thin layer of aluminum was deposited on the surface of the polyester, or mylar. functionally the same as foil, but thinner, allowing for smaller finished size
Orange drops are usually polyester, sometimes foil, sometimes metalized- both work very well, and do not dry out.
Digi-Key has best prices I have found on many of the caps, If you are dedicated to orange drops, they may not have what need, but their catalog is extensive.
:I am replacing alot of the caps in my Radio, mostly the paper ones. I see that in my Vintage Radio Parts Catalogue that there are different types for different uses. I am not talking Electrolytic in this post as I know about them..But names like Metal Foil polypropylene, Metalized Polyester film, Mylar Film, Ceramic, which type are Orange Drops? And then some say coupling and why is a coupling cap different than the above. I know what a coupling cap does but why do I need a special cap for it?? Isn't a cap just a cap?? Which should I use for signal path and if I use orange drops for the whole thing am I going to notice a sound difference?? Please advise...