Laminar air flow is air flow that constantly moves at the same speed, in the same direction. That being said, a laminar flow hood is a device or enclosure, most commonly used in laboratory applications, designed to carefully guide that filtered air and use it to sweep particles in a uniform speed and direction — from the hood’s most treated area (near the filter) to its exit area. 

Cleanroom airflow uniformity and laminar flow hoods are essential to ensuring that sensitive products placed under the hood are always upstream, and therefore suffer little to no contamination. Flow hoods come in two configurations: horizontal and vertical. Both configurations provide effective sweeping action through the work zone and meet ISO Class 5 cleanliness standards, so your application will help determine which is better for your facility. 

In this article, we’ll discuss the differences between horizontal vs. vertical laminar flow hoods, and help you figure out which is best for your application. 

Horizontal Laminar Flow Hoods

Horizontal laminar flow hoods direct air, well, horizontally. The air is pulled from behind the hood, then is pushed through a HEPA or ULPA filter to move forward across the work surface until it exits the enclosure. 

By sweeping the air across the work surface and towards the operator, horizontal laminar flow hoods provide the lowest level of turbulence (random air movements), and therefore the highest level of protection from contaminating particles. This is because there’s no turbulence caused by vertical air striking a perpendicular surface, and no disruption caused by the hands of the operator, since they’re always further downstream than the materials being worked on. 

However, the size of the hood, positioning of the filter, and direction of the air flow can result in some negative consequences, as well. Below, we’ll detail the full list of pros and cons for these types of hoods:


  • Low turbulence on work surface, due to air flowing parallel to work surface
  • Easy to position products and materials close to the filter on the work surface
  • Little contamination from hands or gloves, due to operator being downstream from products and materials


  • Requires hood repositioning in order to gain rear access for filter changes and servicing
  • Large materials or pieces of material can obstruct the flow and contaminate anything downstream
  • Operator could suffer from fume and/or powder contaminants blowing at them if sash is used improperly

Vertical Laminar Flow Hoods

In contrast, vertical laminar flow hoods take air from above the unit, push it through the HEPA or ULPA filter, then direct it downward onto the work surface, where it eventually disperses and exits the enclosure out of a front access area. They resemble the model of a laminar flow cleanroom with fan filter units on the ceiling, just on a much smaller scale. 

Vertical laminar flow hoods are a popular choice because of their size, layout, and operator safety. Since the filter is positioned on top of the unit, rather than behind, these flow hoods require less floor space, but can be taller to fit larger products and materials. Also, since the laminar air isn’t blowing toward the operator, there is much less risk for them to suffer any contaminants. 

Vertical laminar flow hoods are a great choice for plenty of applications, including handling sterile, non-hazardous drug compounding in research labs, pharmacies, and microbiology. Here’s a quick overview of their pros and cons:


  • Requires less floor space
  • Increased operator safety
  • Easy access for filter changes and servicing
  • Less cross-contamination of items on the work surface, due to no parallel air flow
  • Taller system that can accommodate tall and large products and materials


  • May require overhead clearance for changing and servicing filter
  • Increased work surface turbulence, due to vertical air hitting a perpendicular surface
  • Products and materials can’t be stacked without obstructing air flow

Things to Consider: Horizontal vs. Vertical Laminar Flow — Which Hood Is Right for Your Application?

Both horizontal and vertical laminar flow hoods can be used for a number of applications involving sensitive products and materials, including (but not limited to):

  • Injectable drugs
  • IV solutions
  • Tissue culture
  • Optics
  • Microelectronics

While both flow hoods are great options for reducing contamination while working with sensitive objects, there are a few applications that lend themselves more toward one or the other. Usually, the most important factors to consider when making a decision between one or the other include process location, clearance requirements, size of materials, work surface design, and operator safety. 

That being said, horizontal laminar flow hoods generally work best for applications that require minimal turbulence on the work surface and the highest level of object contamination control. They may also be preferred if your product must remain within the work zone for extended periods of time. 

If your application’s process is performed above the work surface, a vertical air flow configuration may be ideal; particles inside a vertical configuration settle at the bottom of the work surface before exiting the enclosure. These are also a popular choice for any applications involving materials that could be especially large in size or dangerous to the operator.

If your cleanroom requires laminar flow hoods, Angstrom Technology can design a cleanroom that will meet your classification and industry requirements seamlessly, whether it’s vertical or horizontal. Contact us to talk to one of our design engineers today.