<p>I have an Ender 3, currently in stock Bowden extruder configuration.</p>
<p>I want to be able to print nylon and TPU, both of which require temperature too high for the tolerance of the PTFE Bowden tube (as well as the issues with the flexible filament in the tube).</p>
<p>Therefore, I've considered converting my printer to direct drive.  However, the conversions I've seen, both DIY/print the parts type and commercial, seem to include a short length of the same PTFE tube between the extruder (now mounted on the hot end carriage) and the actual hot end.  This same material ought to have the same temperature limit (about 250 C) as it would have in a Bowden configuration -- and for nylon, at the least, this is a problem, since the PTFE would start to soften from contact with the heat break.</p>
<p>Am I missing something in these conversions, or is the PTFE's glass transition not the limiting factor in printing hotter with a direct drive conversion?</p>

Direct Drive v.s. Bowden has no relation to the maximum print temperature. What determines the maximum print temperature is the design of the hotend itself. There are "all-metal" designs, where the PTFE tube (Bowden or not) stops in the cold zone and the heatbreak and all other components that get hot are fully made of metal. Other hotend designs have the PTFE tube run all the way down into the hot zone and this limits the maximum printing temperature. It has nothing to do with whether the hotend is Bowden or not.