Caps - when to use el or NP?

[ethrbunny]

Is there a rule-of-thumb for when to use polar or non-polar capacitors?

[petemoore]

You don't want current going reverse through the cap, some positions do this. In these positions use a non polarized cap or make a non polarized cap from two polarized caps.
 Connect the - from cap 1 to the + of cap two, and the + from cap one to the - of cap two.
 +cap  -
 - cap +

[R.G.]

Use electrolytic when you can't either physically fit in a film capacitor or afford it in the value of capacitance and voltage you need.

Use NP (which is electrolytic, just electrolyzed on both sides of a plate, not one) whenever there is either substantially zero DC volts across the cap or whenever signal and operating conditions will cause the voltage across the cap to ever reverse by more than about 0.1V. You really should work electros at a bias of 50% to 90% of their rated DC voltage for long life.