Low leakage capacitors

Hi,

I'm trying to find the lowest leakage capacitor, somewhere in the range of 0.01uF to 1uF, *might* be able to live with 0.001uF, for DC use. I'm not sure if PTFE (teflon) is the best choice, but here's one

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It says, "Insulation Resistance: 1000 M=A5=D8*=A5=ECF Need not exceed 100,0=

Also I heard polystyrene is good.

I've performed various RC time constant tests on caps by placing a voltage source on the cap for a period of time, removing the voltage source and time it, then measure the DC voltage after a certain time period, and calculate the parallel resistance. It appears that the longer the voltage source is held on the cap results in more parallel resistance-- possibly dielectric absorption.

So this makes it more difficult to find the best type of caps for this use. IOW, perhaps one cap might have less leakage after 1 minute, but after 10 hours perhaps another type of cap might have less leakage.

I'm looking for a cap that would contain as much charge as possible for about one day. The voltage levels are around 1 volt.

Any help is greatly appreciated! Paul