The bulb or membrane is constructed of different types of glass, each with different useful properties.
General-purpose glass: various pH ranges, temperatures to 212ºF (100ºC).
Blue glass: pH 0 to 14, temperatures to 230ºF (110ºC).
Amber glass: pH 0 to 14, temperatures to 230ºF (110ºC), prevents Na+ error in high Na+ concentration solutions.
The bulb shape can be modified to provide a semi-dome for increased ruggedness, a spear tip for penetration applications, or even a flat surface.
Epoxy-body electrodes are impact resistant and are ideal for rough handling but should not be used at higher temperatures or for solvents.
Note: Even though the body of an epoxy electrode is plastic, the bulb will still be glass. Glass-body electrodes withstand high temperatures and highly corrosive materials or solvents.