What is heat creep ?
Short answer: Heat creep is something we should not have to deal with on our machines…
Loooonng answer… :
Heat creep happens whenever a filament in the hotend travels slower through it than what the heat from the melting chamber can travel upwards.
In a traditional, old school type hotend/extruder combo heat creep is something most users never encounter(ed).
So the real question should be why BAMBU printers suffer so badly from it…
Weight and speed matter and make a big part of the success story for Bambu.
The downside of such a light head system is that they went a bit too far with the hotend.
To maximise the build volume and minimise the costs for the housing and framework our hotends are very short and come with a heatsink and fan that is close to being useless for certain print applications.
The default for PLA at 0.2mm layers with the 0.4mm nozzle is around 200mm per seconds…
Means in most cases it maxes out the standard max flow rates Bambu sets.
Problem is that the other way around the hotend can keep up - with the cooling that is.
0.08mm layers mean a rather slow print speed if you are after a good quality print.
Check those flow rates in the preview 
While the actual heatsink MIGHT get cold enough with the door open on a cold day - it won’t be able to prevent the filament itself from acting as a heat carrier.
You can check this with a simple test.
Create a small lithophane of about 3.5 to 4mm thickness.
Place it flat on the bed, slice it as solid and check how much filament it uses.
Then create a simple cube that uses roughly the same amount.
Try to print both at 0.1mm layers and with the default settings using some glow in the dark filament…
The cube will come out perfect but good luck with the lithophane…
The reason certain filaments come with a 0.6 or above nozzle diameter suggestion is not only the type of filler used…
The larger diameter means the flow rate has to be much higher than when using a 0.4mm nozzle!
With this the filament has less chance to heat up past the heatsink…
Sadly Bambu has no plans to provide a hotend that is better equipped to deal with heat creep 