1. Why should I do that?
There are basically two reasons to install a silicone sock on your hot end.
The biggest problem with cooling fans is that they are usually flowing cold air towards the hot end and nozzle.
This often causes problems such as “Thermal runaway”.
This is a V5 hot end without silicone sock after one month.
Melted plastic tends to stick to the hot end, especially PETG with it’s stringing tendencies.
It is better to use a silicone sock and keep everything without melted plastic and clean.
Please note that this picture is taken with a Kossel V5 Head, which is the same as in i3 Mega.