If your cap will be used in an oscillator, here are some facts to consider.
(This may not be critical to your application, but it is good to know)
Up to about 10MHz it is often practical to use polystyrene caps. They have a slight -ve temperature coefficient making them ideal to use with magnetic cores with a +ve coefficient.
Silver-mica can also be used but their individual drift characteristic may vary from -ve, zero or +ve (even for caps from the same batch!). The only way to grade them will be to monitor the capacitance with a cap meter for change in value over say a 1 hour period in a temperature chamber when the temperature is varied from about 50-100 deg F.
Once graded they make excellent capacitors for use in oscillators because of their high Q like polystyrene.