Physical Properties of WPI Glass Capillaries

The physical properties of glass depend upon the chemical composition of the glass, as well as how the glass was manufactured. Glass has no set melting point, but four temperatures are of primary importance when discussing glass production.

  • Working Point - This is temperature that the glass is soft enough to work. At this temperature, the glass viscosity is 104 poises.
  • Softening Point - At this temperature, glass deforms easily, even by forces of gravity. The glass viscosity is 107.6 poises.
  • Annealing Point - When glass reaches the annealing point and remains for a few minutes, many of the internal stresses of the glass formation are obviated. During the annealing process, the glass is heated to the annealing temperature and then allowed to cool at a controlled rate. Glass that is not annealed is prone to crack or shatter with minor temperature fluctuations or mechanical shocks.
  • Strain Point - When glass temperature remains at the strain point for several hours, the internal stresses are relieved. Stresses that remain in the glass after maintaining the strain point for a few hours are permanent.

WPI sells glass from multiple suppliers. In the tables below, we will detail some of the common glass specifications.

  Duran® Schott 8250 Duran® Schott 8330 Corning 7800  Kimble N51A 
WPI Usage Pulled Glass PG-52151, PG-52165 WPI thin wall glass capillaries
pre-pulled micropettes with 
TW in the part number
multi-barrel glass capillaries
septum theta
piggyback capillaries
glass rods
single barrel glass tubing
(p/n 1Bxxxx)
Density ρ   2.28g/cm3 2.23 ± 0.02g/cm3 2.33g/cm3 2.33g/cm3
Working Point - 104 dPa·s 1055°C  1260 ± 20°C   1140°C
Softening Point - 107.6 dPa· 720°C  820 ± 10°C 789°C  785°C
Annealing Point - 1013 dPa·s  500°C  560 ± 10°C  565°C   570°C
Strain Point 490°C  510°C 517°C   530°C
Relative dielectric constant 
tan δ at 1 MHz
and 25 °C
  4.6 10-4
37 10-4
Thermal expansion - 0-300°C 5.0x10-6/K 33x10-7 cm/cm/°C  55x10-7 cm/cm/°C  55x10-7 cm/cm/°C 
Young's Modulus 64x103N/mm2 6.4x103Kg/mm2 7.2x103Kg/mm2  10.4x106PSI
Poisson's Ratio 0.21 0.20     
Dielectric Constant 4.9 4.6   5.8
Loss Factor 1MHz 25°C 22x10-4 2.6%    4.9% 
Refractive Index 1.487 1.473mm²/N  1.490mm²/N  1.490mm²/N 
Temperature Limits     460°C (extreme service)
200°C (normal service)
Max. Thermal Shock     115°C  
Visible Light Transmission 2mm thickness       91%
Specific Heat 25-175°C       0.204 g. cals per g. deg.
Thermal Conductivity  1.2W/m/K (at 90°C)     0.0026 cals/cm/cm2/sec/°C 

Corning 7800 glass is a type I, class B borosilicate glass that conforms to federal specification DD-G54lb and ASTM E-438. This glass has the following composition:

  Corning 7800 Duran® Schott 8330
SiO2  73% 81.0%
B2O3 10%  13%
Na2O 2%  ~2.0%
Al2O3 7%  2.0%
K2O 2%  ~2.0%
BaO <0.1%  
CaO 0.7%  


See Selection