Thermoseal Group Limited

Thermoseal Group issues 7 Steps to Selecting a Quality Desiccant

A large proportion of IG unit manufacturers in the UK are under the illusion that if a desiccant is tested by a notified body (for Moisture capacity) and the factory where the desiccant is manufactured has a recognised quality system (i.e. – ISO 9000) that the desiccant is of a high quality. Thermoseal Group advises that this is not necessarily so.

Throughout the life of a sealed unit moisture passes through the edge sealant where the two panes of glass are fixed together. This is referred to as the moisture vapour transmission rate, or MVTR. The desiccant serves to adsorb this moisture throughout the lifetime of the unit so its quality is vital.

Problems in the quality of desiccant can be due to various factors including: its original manufacturing process; deterioration during transport, and ineffective storage methods. Often you can’t detect a quality issue by simply looking at the product, so quality-assurance testing is essential.

A good quality desiccant must have the following 7 properties to ensure that a sealed unit lasts beyond its warranty period:

1) Pure 3A Angstrom Construction
2) A Good Delta-T Test Performance
3) Very Low initial moisture content (Less than 2%)
4) Moisture Adsorption Capacity 16-20% @ 10% Relative Humidity
5) Low Dust Content
6) Very Low Gas Desorption below 50ml water displacement
7) An acceptable bulk density

Thermoseal Group has prepared a full document detailing the above requirements in 7 steps and detailing the tests required. This is downloadable on our website or can be requested by e-mailing

The Group also offers a desiccant testing service, or can supply a test kit so that sealed unit manufacturers can perform some tests themselves. Please visit the Group’s website to see some of the alarming test results performed on some of the UKs widely supplied desiccants. Alternatively, Thermoseal Group is happy for you to visit one of its sites with a sample of a desiccant to be tested while you watch.

For further information regarding Eurosiv desiccant or any other of the machinery and consumables available from Thermoseal Group, call 0845 331 3950 or visit