Efficient and easy way to thermally insulate the heat block of the hotend?
The "quick and dirty" approach is to just slap a bunch of Kapton tape on there. The more the better! (Until you need to dismantle for maintenance, anyway.)

I find pre-cut ceramic tape + kapton tape "blankets" to be easy and effective. E3Dv6 and Replicator 1/2 style hot blocks should be compatible. Or you can cut your own using a sharp hobby knife. 


http://www.fargo3dprinting.com/products/makerbot-replicator-2-ceramic-insulation-tape/

The main downside is that they don't insulate two sides of the hot block. But covering the top and bottom provides much of the practical benefit, and you can always add a few more wraps of Kapton tape to cover up the rest of the surfaces. 

Another good option that has recently started to become popular is fiberglass heat shield tape. It has a silicone adhesive, woven fiberglass mat, and shiny aluminum surface. (The reflective surface reduces heat radiation.) It's often used in automotive applications around mufflers and the like. You can cut it up into little rectangles for each side of the hot block, or wrap the block similar to Kapton. 


https://shop.raffle.ch/shop/insulation_material/

Main issue is quality -- not all brands have adhesive that will hold up to high temp printing. It may smell when initially "burned in" due to the adhesive cooking a bit. I also find that you need a couple layers to get as much insulation as the ceramic+kapton blanket when there's a lot of airflow around the hot block.