KLEN International has its origin in the town of Bunbury in the south west region of Western Australia where it commenced operations in 1971. When it was first established, the firm concentrated on the manufacture of specialty detergents and sanitisers for the food and beverage processing industries. In that capacity it grew to become the premier supplier of specialty detergents to the region.

In 1974, KLEN WA, as it was then known, was purchased by the Perth based McGuire Corporation. McGuire Corp was also a producer of specialty detergents as well as other products such as sealers and fertilisers. Following the successful integration of the KLEN and McGuire businesses, McGuire Corp went on to purchase the small manufacturing and trading operation, CIC Chemicals. CIC was involved in the mining and assay industries and traded in commodities such as Cyanide. However, of far greater significance was its involvement in the manufacture of fire assay flux and the supply of fire assay consumables to the mining industry and assay laboratories.

Following the successful integration of the KLEN and McGuire businesses, McGuire Corp went on to purchase the small manufacturing and trading operation, CIC Chemicals. CIC was involved in the mining and assay industries and traded in commodities such as Cyanide. However, of far greater significance was its involvement in the manufacture of fire assay flux and the supply of fire assay consumables to the mining industry and assay laboratories.

In 1999, the companies formalised their operations under the single trading name of KLEN International which embarked on an aggressive expansion program to take its products to the world. KLEN was particularly successful at building its global reputation as a leading supplier of high quality fire assay fluxes. Over the ensuing years, KLEN developed its market taking the product to all gold producing regions of the world, exporting to over 60 countries. Links were also established with major global laboratory chains and KLEN became a supplier of choice to many of the key analytical companies.

The success of KLEN in the global fire assay market attracted the attention of other laboratory supply companies and in 2012, American based VWR International was successful in acquiring the fire assay division of KLEN International.

In July 2014 KLEN relocated to a new, custom built facility in Neerabup, Western Australia.

In 2017 VWR was acquired by Avantor Inc. KLEN now forms a critical part of the global supply strategy of Avantor and through the group of Avantor companies is in a position to offer a broader product range to fire assay laboratories.