WEE Technology Company Limited - WEE are Capacitors Specialist

WEET tell you how to understand the inner and outer foil of WMH 100V 200V MKP Foil Capacitor Also Called Foil and Film Condensatoren.
Firstly, we can use an  Oscilloscope to test each of the leads, and you will see different waves on the Oscilloscope, please read below article for detailed reference.
http://www.jimmyauw.com/2010/04/24/observing-inner-and-outer-foil-of-some-popular-capacitors/

At the same time, we can refer to below article to understand why you need to know outside of the foil.
http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors

Finally, some factories will mark a line at the outer foil side, WEET can do the same, if customer request for it.