Prosorb Humidity Control - Cassettes

Humidity control cassettes from Prosorb present an easy way of maintaining a stable relative humidity level in display cases and cabinets.

Supplied as a complete unit, the prosorb cassettes require no additional containers or trays. Pre-filled with Prosorb beads, the cassettes are constructed from a sturdy polypropylene case with vapour permeable non-woven polyester panels.

Dependent upon the desired RH (relative humidity) '%' required, we have cassettes preconditioned to satisfy the ideal level for museum display cabinets, generally in the range of 40% to 60%. The enclosed Prosorb beads will absorb and desorb water vapour, as appropriate, to stabilise the humidity.

As with any other humidity control, it is important to monitor the environment using a hygrometer as reconditioning may be required after an extended period. Clay packs are available for reconditioning, see accessories below, for more details see here

Prosorb Cassette Sizes

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

Half-size cassettes:

• Dimensions: L 335 mm, W 110 mm, H 24 mm.
• Content: 500 g beads. One half-size cassette will be sufficient for 0,7 m3 depending on circumstances of application

• Free of chlorides: PROSorb contains no lithium chloride, as some other products do (Lithium chloride is a chemical - salt, potentially harmful to many metals. This salt can be transferred to metals in dust or by human touch). PROSorb consists of 97% SiO2 and 3% Al2O3.
• Low abrasion: PROSorb 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 stability: PROSorb maintains the greater part of its capacity well beyond the 2-5 years when other silica gels have lost a large portion of their capacity.
• Economical: PROSorb is much cheaper than the other products sold for the same purpose.
• Temperature dependency: PROSorb 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.

How many Prosorb cassettes do I need?

The absorption rate of Prosorb full and half cassettes isn't typically described as a single, fixed "rate" in terms of grams of water per hour or day. Instead, their effectiveness is characterized by their capacity to absorb and desorb moisture within a specific relative humidity (RH) range (typically 30-60% RH), and the amount of Prosorb needed per volume of the enclosed space.

Here's a breakdown of what influences their absorption:

• Pre-conditioning: Prosorb cassettes are supplied pre-conditioned to a specific RH level (e.g., 30%, 45%, 60%). This means they are already holding a certain amount of moisture. Their action involves either absorbing excess moisture if the RH rises above their pre-set point or releasing moisture if the RH drops below it, striving to maintain that equilibrium.
• The volume of the exhibition case: The larger the case, the more Prosorb is generally needed to effectively buffer the humidity.
• The tightness of the seal of the exhibition case: A well-sealed case will experience slower humidity fluctuations, and thus the Prosorb will work more gradually. A less sealed case will have more air exchange with the external environment, leading to more frequent absorption or desorption.
• The difference between the internal and external humidity: Larger differences will lead to a greater demand on the Prosorb's capacity.
• The materials within the case: Hygroscopic materials (like wood or textiles) can absorb and release moisture themselves, influencing the overall humidity and the work the Prosorb needs to do.
• Temperature fluctuations: While Prosorb is designed to react similarly to organic materials under temperature changes (minimizing drastic RH shifts), significant temperature swings can still affect the equilibrium.

Instead of a rate, manufacturers often provide guidelines on the amount of Prosorb needed per cubic meter of the display case volume:

• Full Cassette (950g): Typically, one or more full-size cassettes are recommended per 1 cubic meter of air volume, depending on the specific application and the factors mentioned above. We suggest 1-4 cassettes per cubic meter.
• Half Cassette (500g): Generally, one or more half-size cassettes are recommended for a volume up to 0.7 cubic meters.7 Again, we suggest 1-4 cassettes per 0.5-0.7 cubic meters.

Key takeaway: The effectiveness of Prosorb isn't about a speed of absorption but rather its capacity to handle moisture fluctuations within a desired RH range for a given volume and the equilibrium it strives to maintain. The amount you need depends on the specifics of your exhibition case and the environment.

It's always best to monitor the RH inside your exhibition case with a calibrated hygrometer to ensure the Prosorb is effectively maintaining the desired conditions. You may need to adjust the number of cassettes based on your specific needs and observations.