These flame-sealed cells contain a small amount of >98% pure water (H₂O) vapor. The concentration of water in the vapor phase may be controlled by heating the cell or cooling the tipoff stem. Operating temperatures typically range from -10-100°C. Water has a strong vibrational X band absorption which is used for calibration of tunable lasers and wavelength meters in the range of 3450-4000 cm^-1 (2500-2900 nm).

The quartz cell body is cylindrical in shape; outer diameter 19 mm; length 75 mm. The tipoff stem is centered on the cell, protruding not more than 10 mm from the cell body. Windows are angled 11° off of normal and have a 2° interior wedge to prevent back-reflection and etalon effects.