I have what my be a very dumb question. But can someone tell me what the difference is between a .01uF Ceramic Cap and a .01uF Polyester.
I have a project that calls for a .01 Ceramic Cap, but all I have on hand is a .01 Polyester. Can I use it.
You can but where is it?
A polyester is not much good for power supply decoupling as it has a poor high frequency response. However, it is better for signal coupling and it is more linear with voltage. That means the capacitance doesn't change much with applied voltage.
More precisely some polyester capacitors are inductively wound and no good for decoupling
(not all types are like this, but without a means to measure series inductance or the right datasheet
you can assume the worst). Plastic capacitors in general have well defined values and linearity
and are used in analog signal processing (filters, amplifiers, etc).
Ceramic capacitors come in various grades, but in general have shocklingly poor tolerance and
linearity (useless for an analog filter circuit), but are extremely low inductance and perfect for
Ceramic capacitors use ferroelectric crystalline materials which can have extremely high permittivity
values (lots of capacitance for a small size).
0.01uF is not likely a decoupling cap, more likely some kind of signal filtering application.