For museum applications, the most important difference is buffering capacity, defined by the gel's MH value.
• The most commonly available silica gel, referred to in the industry as regular density or RD silica gel, is universally available. Its primary function in industrial use is as a desiccant. Because of its poor hygroscopic properties around 45-50% RH and above, it is not recommended for museum applications requiring control in the mid to upper RH range. Within the range of 40-55% RH, it has an MH value of 2.
• Arten Gel and Rhapid Gel were developed for museum applications because of their high moisture buffering capacities throughout the entire RH range of interest for museums. Within the range of 40-55% RH, they have an MH value of 9.
• Art-Sorb has a high buffering capacity above 60% RH, but has a lower capacity than RD gel or Arten and Rhapid Gel in the lower RH region. Within the range of 40-55% RH, it has an MH value of 4.5. In sum, for an exhibition case maintained within the 40-55% RH range, for each pound of Arten or Rhapid Gel used, twice as much Art-Sorb or more than four times as much RD silica gel would be required for comparable buffering capacity.