Moderately fired, largely Talc body. Made with a time-tested, proven formula, it is a utilitarian ceramic with good porosity, tough exterior and interior surfaces, and is ivory white in color. Recommended for general purpose uses that involve pressure differentials under 1 Bar (14.5 psi). Typical bubbling pressure: 20-30 psi. Effective pore size: 1.7 microns. Hydraulic conductivity: .000000756 cm/sec. Approximate porosity: 34% by vol. Flow through. All cups are "as cast".