<p>The original bed surface of my Ender 3 has become brittle and finally cracked, requiring replacement. I'm trying to figure out what the cause might have been to avoid it happening again. It seems to have started after using "flex PLA", which involves both high temperatures (225&nbsp;&deg;C) and plasticizers mixed in the PLA. Could either of these have contributed to the problem? I'm not sure what material the bed surface is - it's the new one that's removable and held on by clips. If it's PEI, the glass transition temperature is supposedly 217&nbsp;&deg;C, just above what I use for normal PLA but well below what I'm using for the flex, so perhaps that's the cause?</p>

<p>Image of the damage: <img src="https://i.stack.imgur.com/wXWW4.jpg" alt="Image of the damage"></p>

The material used for the Build surface is not PEI but a BuildTak Clone that offers adhesion through a rough surface texture. I do not know what exactly is in the composition of the polymer, but I can say that my bed surface needed replacement about 9 months after purchase after I vigorously removed a piece I printed. As a matter of fact, most build surfaces - even PEI - are pretty much going to wear out over time and need occasional replacement. Luckily, a build surface isn't expensive usually.
To prolong the life of the bed surface, I suggest:
check the nozzle distance to the bed, as printing too close can make plastic residue extremely hard to remove.
be very careful when using sharp tools to remove parts - don't let a corner bite into the surface!
don't use a soldering iron or hot air gun on the build platform to remove stuck parts, you'll melt the surface and degrade it
clean the surface at times.
However, replacing the bed is easy enough, as I found out
here
.