ProSORB Humidity Stabilizer

PROSorb is a silica gel ideally suited for stabilizing relative humidity inside museum display cases and storage cabinets.

The ideal level of humidity for most museum display cases and storage cabinets is a level between 40 – 60% RH (Relative Humidity). It is also desirable to maintain this level for as long as possible.

PROSorb has a unique and exceptional adsorption capacity within the 40 – 60% RH range (see graph to the right), and surpasses all other products sold for this purpose.

PROSorb is able to maintain a stable RH within narrow margins through its ability to both absorb and desorb water vapour; and is provided pre-conditioned to your desired humidity level

PROSorb also has a longer life span than other silica gels.

Further advantages of PROSorb

  • Free of chloridesPROSorb contains no lithium chloride, as some other products do (lithium chloride is a chemical – a salt, potentially harmful to many metals. This salt can be transferred to metals in dust or by human touch). PROSorb consists of 97% SiO2 und 3% Al2O3.
  • Low abrasionPROSorb beads produce less dust than other silica gels (abrasion< 0.05 weight-% according to MIL-D).
  • High bulk density: 1 kg PROSorb only needs a volume of ca. 1.5 l (much less than some other silica gels).
  • Long term stabilityPROSorb maintains its adsorption capacity longer than other products. After 10 years we found adsorption capacity of PRO SORB to have decreased by around 20%. In other words: PRO SORB conditioned to 50% RH and maintained at constant weight (e.g. sealed in an aluminium bag) would increase its conditioning by around 0,8 – 1 % RH per year (experimental values after 5 and 10 years). Values might depend on ambient conditions.
  • EconomicalPROSorb is much cheaper than the other products sold for the same purpose.
  • Temperature dependencyPROSorb  is conditioned in relation to temperature. PROSorb reacts in the same way organic materials do. Therefore there will be no, or little, transfer of water vapour between organic materials and PROSorb if the temperature changes. Under fluctuating temperatures, this property protects wooden objects and other organic materials from swelling or shrinking: The conditioning indicated on the labels refers to 20°C. At 10°C the conditioning of the cassettes will be around 1 – 1.5% RH lower, at 30°C around 1 – 1.5% RH higher.

Further technical data

Bulk density ca. 0.7 kg/l
Pore volume ca. 0.5 ml/g
Breaking strength over 200 N
Internal surface area ca. 750 m2/g

PROSorb cassettes and sachets:

PROSorb cassettes are easier to handle than beads. They don’t need trays or containers and are quickly exchanged quickly. Re-conditioning their RH-value can be done easily by weight within the first 1 – 2 years. After a longer period of time, due to the slow degradation shown by all types of silica gel, conditioning must be checked with a calibrated hygrometer. The cassettes consist of sturdy PP and vapour-permeable non-woven polyester. They are filled with PROSorb beads.

PROSorb full-size cassettes

Dimensions: L 335 mm, W 110 mm, H 44 mm. Content:  950 g beads. One or more cassettes per cubic metre of air volume are required, depending on circumstances of application (see: PROSorbdirections)

PROSorb half-size cassettes

Dimensions: L 335 mm, W 110 mm, H 24 mm. Content:  500 g beads. One or more cassettes per 0.7 cubic metre of air volume are required, depending on circumstances of application (see: PROSorb directions)

PROSorb sachets, dust-proof

Made of LDPE film and TYVEK 1073, (non-woven PE, dust proof, sturdy, vapour-permeable).
Everything made to your requirements: dimensions (up to 35 x 35 cm), content in grams, conditioning. The sachets are stamped with content, conditioning and weight, so you can use them like cassettes.


Thickness: 10 or 20 mm. Dimensions up to 600 x 1150 mm, conditioning 35 – 60% RH. Sheets are only produced on order.

Material. PP-honeycomb, lined on one side by a polyester non-woven, on one side by Marvelseal 360
The 10 mm sheets contain ~ 3,5 kg PRO SORB / m². Total weight ~ 5 – 5,5 kg / m² depending on conditioning.
The 20 mm sheets contain ~ 7,5 kg PRO SORB / m². Total weight ~ 10,5 – 12 kg / m² depending on conditioning.

Honeycomb sheets and their polyester lining have been Oddy-tested in 2011 and are safe for permanent use in museum showcases. The aluminium film Marvelseal is being heat-sealed without addition of any further products. The Marvelseal film is bent around the edges and covers ~ 10 mm of the front side as well. The outer 10 mm of the sheets don’t contain any PRO SORB – they can be used to to fix the sheets to a wall etc. The edges are re-inforced with Oddy-tested aluminium tape 3M #425

Conditioning, weight and year of production are indicated on the back side of each sheet. We deliver the sheets sealed in aluminium film.

Round sheets or any other shapes are possible upon request. Just send us your drawing and ask for a quote.

The sheets are not completely dust proof. So don’t use them above works of art!

PROSorb beads and cassettes can be ordered, with no additional charge, conditioned to the following RHs:  35%, 40%, 45% 50%, 55%, or 60% RH (please indicate along with your order). Conditioning refers to 20°C, with a tolerance of ±2% RH.