📍~100% of tiny particles (<0.1μm) through Brownian diffusion
📍~100% of the larger particles (>1.0μm) through interception
📍medium particles (~0.3μm) are trickier but an N95 mask will still filter out 95% of these.
To understand this in more detail, this brilliant video from @minutephysics explains the genius physics behind N95 masks and how they work to protect you against even the tiniest fine particles.
TLDR: They work more like magnets than like sieves.
There are a number of mechanisms in action within N95 masks which contribute to their filtration efficiency, including:
Oh, and just in case you’re getting confused about all the mask terminology (N95, N99, FFP2, FFP3 etc), this is a really useful explainer from the good folks @SmartAirFilters:
Broadly speaking, an N95 is similar to the European FFP2 standard.
Analysis of NHS data by the RCEM, shows that from Jun-Sep 2025, over HALF A MILLION patients had an A&E stay of over 12 hours from their time of arrival in England.
This is MORE than the entire winter of 2021-22, during which the UK experienced one of the worst Covid waves.
In the latest weekly figures, there were 188 people Covid deaths across the UK.
“It's an uncontroversial statement from an epidemiological point of view to say that improving ventilation in schools would be a good thing […] The advantages of ventilation are very substantial.”
So why aren’t we doing it?
Data from the national schools air quality monitoring project (SAMHE) shows that ventilation rates in schools drop to just 3.8 litres per sec per person in colder weather.
This is far BELOW the minimum UK guidance of 5-8 litres per sec per person.
For more clips from Prof Chris Whitty’s appearance at the Covid Inquiry today, please take a look at this excellent thread from Clinically Vulnerable Families (@cv_cev):
Why do schools need to tackle poor VENTILATION in classrooms?
Because nationwide monitoring of UK classrooms shows that ventilation drops to appallingly low levels when outdoor temperatures drop & windows are closed.
Poor ventilation means airborne viruses spread like wildfire.
Meanwhile, more than 500 children a day in England are being referred to NHS mental health services for anxiety, more than DOUBLE the pre-pandemic rate…
…and yet, the impact of repeated COVID infections on children is never even considered as a contributing factor.