A new company, R-Shield, launched a Kickstarter to make a wearable air filter, that incorporates a fancy nano-thingy to filter the air you breath. As a new company, offering a new health related product, the image of the classic snake-oil salesman the FDA was created to stop springs to mind, but their material assures us this has been tested by a reputable source:

THE MEMBRANE IS A FOUR-LAYER LAMINATE WITH AN INNER LAYER FORMED BY HIGH-DENSITY NANOFIBERS.THE RESPILON®57EFFICIENCY OF THE FILTRATION OF MICROORGANISMS AND PARTICLES HAS BEEN TESTED AND PROVEN BY NELSON LABORATORIES (USA).FILTRATION EFFICIENCY OF THE WHOLE ANTISMOG SCARF HAS BEEN TESTED AND PROVEN BY ENGINEERING TEST INSTITUTE (CZECH REPUBLIC).DESPITE THE HIGH DENSITY OF NANOFIBERS,RESPILON®57 IS QUITE AIR-PERMEABLE AND VAPOR-PERMEABLE,WHICH INCREASES THE COMFORT OF THE PRODUCT AND ENABLES EASY BREATHING OF THE USER ALSO WHILE RUNNING, BIKING ETC.
https://www.r-shields.com/data/home/files/RESPILON_Technical_Data_Sheet_R-shield_2019_02.pdf

Easy breathing while running and biking? Above the others, that is quite a claim.

My experience with wearable air filters

1. Respro masks: I've used several models while commuter/sprint cycling in London rush hour traffic, all year round.
2. N95-certified masks: used while in 'fire season' in the SF Bay Area.
3. MSA Millenium respirator: used while in 'fire season' in the SF Bay Area. This is my 'gold standard', as I have a mask with a good fit (full seal around the face), and change the cannisters on an appropriate schedule.
4. Respilon: primary test while cycling up Claremont Avenue in Berkley during rush hour, or about 30m of a 10% gradiant next to idling cars.

Quantifying the above air conditions:

• London: it's crap. (source
• SF Bay Area fire season: the measurement of PM2.5 trundles up to about 160 when bits of California burn, comparable to Shanghai.

So what was the Respilon like?

Air Quality

My principle test is non-scientific and highly subjective, but when wearing a good air filter, the air one breathes in tastes and smells of nothing. Why? Everything has been filtered out. One then starts to taste and smell oneself, and when one removes the mask, one can taste and smell the air around one again.

Whilst wearing the Respilon next to idling cars, pushing an average heart rate of about 150bpm, maintaining about 220W of pedalling power, I did not notice the pollution they were putting out to any degree.

Having just moved into a dusty house in a very dry parth of the world, I noticed I woke up with a sore throat: I've been wearing the mask partly to increase the humidity of the air I'm breathing (exhaled air contains water, the percentage varying greatly) as it traps some outbound humidity, and partly to filter out the dust. When making my morning aero press of Timeless coffee, I was deprived of the smell of the brewing coffee, despite standing directly over it.

TL;DR? Subjectively, the air filtering is excellent, on par with other products. While not as good as the MSA Milleniun, it also only weighs a few grams, where the Millenium establishes a full-face seal and uses a full cannister aimed to filter our chemical, biological and radioactive agents. Unlike the Respro filters, which are a neoprene (sweaty) shell to hold the filter in place, the Respilon wins on portability and convenience.

Breathing while working hard

Here, the Respilon falls behind the Respro masks, primarly as they have valves to ease exhalation. After about 20m of hard work, I had to pull the Respilon down, rendering it useless, as it felt like I was beginning to suffocate. I have not experienced this with the Respro filters.

Despite being heavy and cumbersome, the MSA respirator is designed to be used by people working hard: wearing protective quipment (ever worn an NBC suit?), carrying heavy equipment, in a stressful situation, and especially with experience, doesn't significantly impede breathing.

TL;DR?

The Respilon is a superb portable filter, that can easily be carried in a pocket or a bag without noticing it until needed. If I want to exercise in poor air quality, I will either use my MSA or Respro masks, due to the better air flow.