Granular versus Bonded Carbon Filters

Activated carbon filters are constructed in two main styles, granular multi-layer free fill and bonded filters, each of which serves different purposes in the containment industry.

Granular multi-layer carbon filters contain loose fill carbon media layered to meet specific filtration needs. Granular carbon media is filled into a solid filter frame which allows minimal media settling for optimal airflow through the loose carbon fill. Granular activated carbon filters can contain carbon impregnated for a single target analyte or can be layered with carbon impregnated for a number of analytes, increasing the range of containment. Granular filtration maintains the original physical and chemical properties of the carbon and offers the greatest amount of surface area for chemical bonding sites.

Bonded filters utilize the same granulated carbon as loose-fill carbon filters, but use various chemical processes to bond the carbon together into a solid matrix, creating a rigid carbon filtration system often used for its convenience of handling. Bonded filters are typically claimed to be “dust-free” because the carbon particles are bonded together in a solid form and can be impregnated with the same chemicals as granulated loose carbon.

Independent Testing

Independent test results indicate some negative effects of bonded filters. Under similar laboratory settings, granular carbon filters maintain safe operating conditions for a longer period of time than bonded carbon filters. Bonded manufacturing causes some of the pores on the carbon (sites of reaction) to be crushed or destroyed, which decreases the adsorption capabilities. This can lead to additional negative effects, including a noticeable pressure drop in the fume hood and less efficient air filtering capabilities over the life of the filter.

To learn more, examine this white paper discussing the differences between granular and bonded carbon filters.


Some processes and procedures do not produce harmful vapors but instead create harmful particulates. HEPA filtration protects the operator from particulates through self-contained filters designed to physically capture particles larger than 0.3 microns with >99.995% typical efficiency. ULPA filters can capture particles as small as 0.12 microns with >99.995% efficiency.

When used in a ductless fume hood, the cabinet is applied as a Class I Biological Safety Cabinet to protect the operator from particulates. When used in a laminar flow cabinet, the process/samples are protected from contamination by maintaining cleanliness within the work zone.

Learn more about HEPA and ULPA filtration choices.

Filter Maintenance and Replacement Program

Carbon filter life can be increased drastically by good housekeeping practices. Cleaning up chemical spills and solvent-soaked cloths that produce large amounts of hazardous vapors can help manage filter capacity over time. Furthermore, regular replacement of carbon filters can help protect personnel and the environment from saturated filters. Many manufacturers and equipment service organizations consider it best practice to change ductless carbon filters at each inspection. The industry accepted Control of Substances Hazardous to Health (COSHH) regulation requires inspection of equipment at intervals no longer than 14 months.

Learn more about filter life and a filter safety program.

Filter Guide

Ductless fume hoods come with numerous advantages when used correctly. Learn more about filter capabilities to ensure your next ductless fume hood is the best equipment for your laboratory.

Filter Reminder Programs

Managing all of the carbon filters in a busy laboratory can be complicated. A filter reminder program is an automated program that reminds laboratory managers and technicians to change their filters on a regular basis, ensuring that each filter is changed prior to full saturation. This helps keep personnel and the environment safe from over saturated filters.

Learn more about a high quality filter reminder program here.