What methods does everyone use when switching between filament types in order to avoid charring the filament.
I use the extrusion/melt temperature ranges as a guide. Like filament types I just switch them. For example PLA to PLA or ABS to ABS, etc., I keep the same nozzle. I can even get away with switching my PLA based Bamboofill with regular PLA because they are the same temperature range. I do need to watch my nozzle diameter here as 0.4 is the smallest diameter I think you can use without clogging it up. I have dedicated nozzles for PVA, NinjaFlex , and clear filaments. For clear filaments, even after purging well when switching you can still get random streaks of the previous color that come out many layers later so I just have a dedicated nozzle for it.
If you do not have at least a 20-25 C crossover in the melt temperature range I would not try swap them out in the same nozzle. Just asking for trouble.
@Jeff_Parish How do you clear the nozzle begore stitching dissimilar materials. I have never successfully done a cold pull
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@Thomas_Cox Did you mean switching or stitching? Not quite sure now what you are trying to do. What type of system/setup do you have?
I have dual nozzle extruders if I’m wanting to print dissimilar materials. Even then there are limitations. Some materials don’t stick to other materials so there still needs to be some basic compatibility between the filaments you are printing with in the first place.
I don’t do cold pulls on my nozzles to clear them. When switching to a dissimilar material on a single nozzle set up I warm up the nozzle and pull out the filament. It leaves a little bit of filament inside the nozzle but that is not a problem. After it cools down enough I un-thread the nozzle and thread in the one I have designated for the new material I have selected. Any material left in either nozzle from a previous session gets purged out with the same or a similar material.
@Jeff_Parish you answered my question.
I recently messed up a hot end due to nozzle leakage out the back side and don’t feel like doing it again.
Ok, hope it helped.
Done that before. 
Q-tips come in handy when cleaning up a hot end while it is hot in those cases.
@Jeff_Parish no this one was thoroughly ruined. By the tim I had noticed it the plastic had fully wetted the insulator sock and coated basically the entire hot end in a plastic rock.
I always manually push filament through while hot,then once a bunch comes out, I pull it out fast. Then out new filament in until it comes through tip and purges all the old color filament out and extrudes clean in the new color.
@Brook_Drumm I do the same, and I usually end up with a little arrowhead on the end of the filament, the depending on the filament Im teplacing , I’ll either use the new filament, or a special “cleaner” filament (if switching filament types i.e. PLA -> PETG) to purge the old filamamt from the nozzle.
The cleaner filament has a large range of temps it works with, it flows with PLA temps, but still has the same viscosity at PETG temps, so while the hot end is getting up to temperature for the PETG I’m able to purge it with the cleaner filament, then I’ll just run the PETG through to purge the cleaner.
I’m using genuine E3D hot ends so there are no PTFE liners.
@PrintinAddiction That sounds like a great way to do it. I’m fairly certain that it was nozzle switching that really led to this.
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@Thomas_Cox Ouch! Yeah, once I tighten the nozzle to the heat block, I try my best to leave it alone, unless I get a bad clog that requires a disassembly.