Pug duct seal - experiences

I've just put together my Peltier cooled system. I went hunting for sealing string as it seems like an ideal material for insulating areas that neoprene can't reach. While I knew what I wanted, I couldn't find it anywhere. What I did find though is something that I believe is called Pug Duct Seal (generic name, brand name unknown). This is a gray clay-like material sold in 1lb blocks for about 3 $ Canadian at Home Depot. I picked up just a small chunk from a friendly HVAC technician for free. It seems absolutely perfect for sealing up my system. Easily molds to my block, doesn't seem like it'll ever degrade, etc.

Just wondering if anyone else has had experience with this material and if there's any disadvantages to its use?

I think I know the material you are talking about. I have had a box with some if it in my workshop for a good 15 years and no, it doesn't seem to decay. It sure does get sawdust stuck in it though. If we are talking about the same material though, I don't think it is a great insulator or even sealer for that matter.

I like to use this black rubber/tar like material that is ment for attaching glass to things. It is cheap,easy to shape and sticks to things like you wouldn't believe (if you stick wood together and rip appart, the wood tears) You can find it at any hardware store or canadian tire or glass shop.