C1457 Simple stupidity

Ye Cheng thought that it was possible that there was plastic in the original manufacture of hollow valley! But why are there so many gels here?

"You can retreat outside and wait. I'll open the tunnel, then you can come in."

If it was just a simple plastic wall, it would have been easily melted by the flames, but under the high temperature of the flames, the black wall just seemed to soften