All PPE mask filters work by filtering out particles as they move through the chaotic structure of a non-woven material. Particles get trapped as they are forced to make twists and turns through the dense network of the material’s fibres. Filtration is also enhanced by an electrostatic charge within the fibres that attract particulates as they pass in the hope of catching them.
Ninety nine percent of certified respirators and surgical masks produced worldwide use traditional filters made from meltblown microfibres, which is a respiratory filter technology that has been in use since the 1980's. Today, electrospun nanofibre filters represent an evolutionary leap forward in filter technology, outperforming meltblown microfibre filters in every key area, including protection, breathability and longevity.
From a technical standpoint, nanofibers achieve this superiority primarily due to three factors:
The goal of this article is to compare nanofibre filters to the meltblown microfibre filters used in 99% of FFP2/FFP3 respirators. However, we have also covered cotton filters as they are currently seeing widespread use in face coverings.
Firstly, we’ll take a look at cotton filters, commonly seen in face coverings and non-certified masks. The images below were taken using an electron microscope and have been magnified 2000 times.
It is commonly known that cotton masks are helpful in limiting the expulsion of large droplets from the wearer. This means they have played an important role in controlling the spread of the Covid-19 virus. However, cotton masks do not offer protection for the wearer. Importantly, they also do not actually block the smallest viral particulates coming from the wearer.
Cotton masks and face coverings are primarily chosen due to their customisable appearance and ease of supply.
Some producers have added add active ingredients to their mask materials with ISO certified anti-viral properties. In these cases, it is important to note that without certified filtration as professional PPE, a mask is unlikely to offer protection against viral particulates, regardless of anti-viral properties in the material.
The meltblown microfibre filter shown above will try to catch the viral droplet by using an electrostatic charge to attract it towards one of the larger fibres. This is similar to the process that makes hair stick to a balloon. This process works well under optimal conditions.
However, the problem is that moisture wipes out the static charge within the filter material, and human breath is almost entirely water. This means that increasing humidity inside the mask after just 30mins of use can cause the meltblown filter to lose 40-60% of its filtration ability. There is also no guarantee that the lost static filtration ability will return if the mask is removed and dried out.
Traditional Type IIR, FFP2 and FFP3 masks were not designed to specifically block viral threats, so their filters are not tested against viruses as part of certification. Viral droplets behave differently to other particulates and can be more difficult to filter. In fact, to be certified as FFP3, a respirator only has to prove it can block particulates that are 360 nanometers and larger, whereas SARS-CoV-2 (Covid-19 virus) particulates are less than half that size at between 80-150 nanometers. For comparison, the RespiPro VK nanofibre respirator has been proven to block particulates to an FFP3 level all the way down to 60 nanometers.
When compared to nanofibre filter technology, a traditional meltblown microfibre filter is thicker and heavier and suffers from a lower porosity (has fewer breathable pores). This means that air physically has more difficulty passing through a meltblown filter.
Nanomaterials filter the smallest threats such as viruses or super-fine industrial particulates exceptionally well simply because they cannot get through the nano-pores.
For example, the size of a nanofibre pore is 5-10 times smaller than the smallest Covid-19 particulates. Respilon® nanofibre filters are specifically tested against viruses with up to 99.9% two-way filtration confirmed.
Nanofibre also has a stronger electrostatic charge which it holds for a significantly longer time, this means it attracts and holds onto nearby particles with greater strength. This ability plus the mechanical filtration ensures consistent two-way protection throughout the life of the filter, no matter how humid the material gets.
Nanofibres dissipate humidity and heat better than traditional fabrics and are more porous with a greater surface area. This reduces air resistance, providing incredible breathability.
Nanofibres use less material to produce and are extremely light. Every Respilon® respirator is highly durable but weighs less than a piece of A4 paper. In fact, one gram of RESPILON® nanofibre could create a string long enough to stretch around the entire Earth, and 10 grams could stretch a line to the Moon!
Whereas traditional certified respirators are thick and have a rigid shape, the light weight and extra flexibility of nanofibre means that it is possible to create a new generation of respirators that can follow the contours of the human face for a better fit with greater comfort.
From a technical standpoint, the properties of a nanofibre filter make it perfect for protecting the mouth and nose of a human being. The key take-away here is that due to superior filtration, breathability and resistance to moisture, a mask containing a nanofibre filter can offer better protection and comfort. Of course, it’s important to note that the level of protection also highly depends on the design and fit of the mask it’s being used in. From an environmental point of view, nanofibre production uses no water and less materials to create.
For the most part, producers of protective masks have yet to embrace nanofibre; their long-established techniques are (understandably) deeply entrenched, so it would be a significant shift to pivot into a new technology in any meaningful way without risking current investments. As with any industry, it can be safer to prolong the use of standing technologies where the returns are guaranteed. Think diesel vehicles VS electric.
Nanofibre filters outperform and supersede meltblown microfibre filters in a manner akin to the way DVD's dominated video tapes in the early 2000’s. The fact that nanofibre is more efficient at blocking smaller particulates, together with greater awareness of deadly viruses and the air-pollution health crisis, means that it’s probably only a matter of time before we start to see the mask market shift towards the enhanced protection and comfort of nanofibre technology.