As cvbrg noted this type of glass has following properties:
You will need to remove touch electronics and plastics which is simple to do.
- Thin, yet flexible tempered glass
- Scratch-proof (scratch-resistant, it can be scratched with diamond or tungsten carbide tip scribers)
- Great thermal conductivity (for uniform heat distribution)
- Very low thermal expansion/distortion (at the usual printing temperatures of 110-120C)
- Resistant to pretty much all solvents (Acetone safe)
- Pretty cheap (around $15 on Amazon)
- Not too hard to hack it into a build plate (see instructions)
Detailed guide:
http://www.instructables.com/id/IPad-glass-as-3D-printing-build-platform/?ALLSTEPS