Polyester capacitors use layers of metal and polyester or Mylar dielectric to make a wide range of capacitance values but normally within a relatively small package and for low voltages. The use of "rolled" film layers lead to high dissipation and capacitance vs. temperature problems.
you can wire an electrolytic capacitor backwards
Polyester is the most common and oldest dielectric in use today. Capacitors manufactured
with polyester film are:
Smallest in size
Have a wide operating temperature range (125°C)
High dielectric strength