Seoul Slug Isolation?

How essential is it to isolate the seol's slug from a negative contact? Will Arctic Ceramica do the trick?

I use a thin layer of nail polish. This work very good in my Mag LED mod.

I use Arctic Alumina Ceramic since it works well with conducting heat away from the slug and at the same time isolates it.

Unless the mounting pad is electrically isolated (as it seems to be on Luxeon stars) or connected directly to the LED cathode (+) terminal (not likely), insulating the LED is essential. If you'll be running the LED at anywhere near its rated current, you should use something that's a very good thermal conductor. Arctic Silver epoxy is the best I've found. Arctic Alumina epoxy is about half as thermally conductive, but adequate. I looked into Kapton tape, but it has only about 1/50 the thermal conductivity of Arctic Silver, so isn't good to use. Whatever you use, you should use the thinnest layer possible that still provides insulation, to minimize the thermal resistance.

c_c

A very good alternative to a layer of thermal epoxy (which is itself far better than nail polish) is an anodized heat sink. Of course if you're doing a mod you don't necessarily have this option.

Looks like I'll be taking a crash course in home brew anodization