Sparked by this question, I wanted to discuss the most efficient and also the easiest ways of thermally insulating the heat block of the hotend.
I have seen Kapton tape insulations as done here with a very conclusive resumee about its usefulness.
In the links of the named article, a method with insulating material from a heatbed is described, however without giving quantitative results.
Additionally, I know that in the guys over in the german reprap forum produce their own silicon covers for the heater block. As I understand there is a large spread between people's reports, from 'almost negligible' as insulator (but helpful for other things) to very useful. No quantification, though. Also, these seem to come with a certain amount of effort to produce.
Are there additional solutions and/or comparisons between solutions?
I just came up with my own solution before I read this discussion. (Monoprice Select v2.1 - Wanhao i3 Clone).
I ~think~ I have a Mk8 hotend.
I had some silicon rubber sheet (about 1.4mm thick) which started life as a cookie sheet, but I gave it a new purpose in life, LOL. I cut two pieces to length to wrap around the hotend, and made a double thick sandwich.
I then used adhesive backed aluminum ducting tape* (SEE EDIT BELOW!!) (NOT duct tape, ALUMINIUM tape) and wrapped the sheets in it, then used needle nose pliers to shape it to fit the heater block. The aluminium tape helps it hold shape.
I used 3M 468MP to tape it to the hotend, as I currently have no kapton tape. Just did this today, if I have adhesion issues I'll TRY to remember to report back here. :) If it does pops loose, I'll use a bit of stiff wire twisted around to support it.
EDIT: Welllll ... sometimes one gets too clever for their own good!
USING THE ALUMINIUM TAPE IS NOT A GOOD SOLUTION, DON'T DO IT!!! It seems the adhesive on that tape emits noxious, and perhaps POISONOUS fumes when heated! I had to vent the room to the outside for a couple hours with dual fans and the hotend at temp to clear the air! Ooops. LOL
It's good now, it baked off.
The idea DID work, and I'm sure would be fine if you use regular heavy duty aluminium foil. Be sure to mount it with the seam on the INSIDE and the 3M tape should hold it closed just fine.