Frequently Asked Questions
Silica gel is a reusable drying and dehumidifying agent (known as a desiccant) that adsorbs and traps water vapour to effectively prevent rust, corrosion, mould, mildew, spoilage, fogging and condensation when used within closed spaces.
Unlike some other desiccants, silica gel does not become wet, or swell in size as it adsorbs moisture. It is also non-corrosive, odourless, chemically inert, does not form by-products and is nearly harmless. In addition, silica gel can adsorb up to 1/3 of its weight in moisture before needing reactivation.
Moisture trapped within a product package or leaking into it during storage and shipping can result in harm to the item. The maintenance of their physical product integrity, as well as the stability of many pharmaceutical formulations and diagnostic reagents, is often closely tied to the moisture conditions of the package environment.
In poorly sterilised situations, moisture may promote the growth of moulds, mildews and fungi. Products that use polymers are prone to swelling in high humidity conditions, due to water causing intermolecular bonds between polymer chains to weaken.
Moisture in electronics causes corrosion and may lead to "short" circuits and other faults. Usually this will not produce sparks; the effects are subtler, and the device may operate unreliably - sometimes it will work, sometimes it won’t. A situation like this is frustrating, time-wasting and may ruin an expensive instrument.
The best way of reactivating silica gel is with the oven drying method, which is as follows:
- Pre-heat oven to 105-115 degrees C.
- Place silica gel in an appropriate metal or glass oven-proof tray - try and keep the silica gel layer to a thickness of less than 2 inches as this allows it to dry faster and more evenly.
- Once the oven is at the correct temperature, place the tray of silica gel into the oven. After approximately 1-2 hours, the silica gel should be dry – if you are using indicating silica gel, it should have also returned to its original colour.
- Wait for the silica gel to cool before handling it as it will be extremely hot. Once cooled, it can be placed back in the moisture barrier bag that it came in, or in any other air-tight space.
Silica gel, when used in a sealed environment can safely be said to last between 4 and 12 months but varies based on factors such as the volume of the environment and how dry the contents that you’re protecting are. Additionally, silica gel won’t last as long if the environment is not air-tight, or is frequently exposed to outside air, i.e. the container is frequently opened and closed. If left out in the open with a relative humidity of 75%, it will take 5-6 hours before the silica gel is fully saturated.
Indicating silica gel contains an indicating dye which will change colour as the silica gel adsorbs moisture, giving the user a visual indication on how ‘full’ the silica gel is. The most commonly used dyes are cobalt chloride and methyl violet, which in turn create blue & orange silica gel respectively.
Blue silica gel will turn light pink when it is close to saturation and orange silica gel will turn dark green when it is close to saturation.
Non-indicating silica gel contains no indicating dye which is evident by its white or clear appearance.
Depending on the relative humidity and outside temperature, silica gel will adsorb between 25% and 40% of its weight in moisture. The higher the relative humidity, the more moisture the silica gel is able to adsorb before reaching capacity. For example, at 25 degrees C and 50% relative humidity, silica gel is able to adsorb approximately 28% of its weight in moisture. At the same temperature, but at 100% relative humidity, silica gel is able to adsorb 38% of its weight in moisture.
Silica gel is most effective when used within an enclosed environment, such as that of an air-tight container or barrier bag. If used in an environment where new, potentially humid air is frequently exposed to the silica gel, the gel will become saturated with moisture much faster, which in turn will require more frequent reactivations/replacements.
These are estimates and relate to situations when used in an airtight environment. The amount of silica gel required will depend on several factors including: volume of contents of the container, the chemical characteristics of the product, physical properties of the container, and conditions in which the container will be stored and used.
For a well-sealed space, it is suggested that 1 gram of silica gel is needed for 1 litre of volume - assuming that the space was moderately dry when the silica gel was added.
Silica gel can be used where processes and products need to be protected from the negative effects of humidity & moisture, such as:
Tool Boxes • Gun Safes • Camera Gear • Electronics • Food & Grain • Breathing Filters in Transformers • Leather Products • Collectibles • Silos & Storage • Laboratories • Jewellery • Camping Gear • Sporting Gear • Fishing Gear • Hunting Gear • Seeds • Clothing • Wardrobes • Telescopes & Optics • Photos • Documents • Musical Instruments • Silverware
Silica gel should always be kept in an air-tight environment. If silica gel is left in an environment that is exposed to new, potentially humid air, the gel will adsorb this moisture and eventually become saturated. Although the moisture uptake rate is not fast, silica gel should not be left open to the atmosphere for longer than 15 minutes.
Silica gel contains millions of microscopic pores which give it a low vapour pressure, making the beads hygroscopic – that is to say, they adsorb water molecules from humid air, which has a higher vapour pressure.
So, when silica gel is placed in a closed, humid container (with high vapour pressure), the water molecules in the air will eventually be adsorbed into the pores of the gel (with lower vapour pressure), because in closed systems, pressure will always try to distribute itself equally.
Silica gel will stop adsorbing moisture when equilibrium is reached, and the water vapour pressure is equal in the gel and the air. Logically, the more humid the air is, the more water vapour will also be adsorbed before equilibrium is reached. Silica gel will also stop adsorbing moisture if it reaches its capacity, at around 1/3 of its weight.