I was interested to examine what difference insulating the hotend heater block would make to hotend performance. I used some Teflon sheet material [ptfe] (sandwich toasting bags!), cut it to shape and then secured it in place with some kapton tape. I've done this in the past as you'll see from this post, but I've never done a graphed comparison of "before" and "after" insulation.
Photo above showing J-Head hotend with newly insulated heater block.
For comparison purposes I dug out a graph of temperature (Deg C) and power (%) over time (minutes) which I had recorded for the same hotend without insulation, while heating to an arbutrary target of 220 Deg C. The J-head was fitted to the printer and both fans running, one under-carriage fan, and the print cooling fan. This graph is below, Temperature over Time in Red, and % power to heater in Green, no insulation on heater block for this graph.