Stolen makes four basic grades of cap, in ascending order: metallized polypropylene (black), tin foil and polypropylene film (white), metallized teflon (blue), and tin foil and teflon film (green). They sound very different.
Metallized poly is the least expensive of the audiophile grades. It sounds relatively smeared. Tin film and foil is a big improvement in clarity, but this may not suit your system as a whole. I find that teflon adds a slight edge, which may make your system unlistenably sharp, or much more life-like, or something in between. As ever, YMMD.
In critical applications I divide the critical value into 3: 1/3 Solen teflon f&f, 2/3 styrene. This gives me a slight edge from the teflon, and a slight rounding from the styrene, for a pleasingly neutral sound. Unfortunately Solen does not sell styrene.
Not only would I do it, I have done it. As you can infer.
