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I saw this type of face masks on a 'building tools' store (like home depot), and on the label said, among other things in chinese and english, non medical.

In this KN95 Masks Explained mentions

These masks, like NIOSH N95 masks, provide protection from 95% of particles that are greater than .3 microns in diameter.

However do they also protect even when says non medical?

Update

I've got one and as you can see the only difference with a medical mask is the FDA label (notice the upper RHS, there is none), as pointed out by @BobE. The brand is exactly the same.

enter image description here

inside the cover was this paper

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Here is the pic with the FDA label (notice the upper RHS, the FDA label)

enter image description here

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    Any mask is certainly better than no mask. – user253751 Aug 10 at 17:10
  • @user253751 In general yes, however a mask made by vacuum bag filters can irritate lungs, as said by LangLangC's answer on Skeptics – I likeThatMeow Aug 10 at 17:49
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    @SnakeDoc That is incorrect. Studies are accumulating which show that masks have a protective effect for the wearer as well: npr.org/2020/07/20/893227088/… nytimes.com/2020/07/27/health/coronavirus-mask-protection.html – Lawnmower Man Aug 10 at 20:43
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    @SnakeDoc, evidence is accumulating showing that the smaller the initial dose, the more likely it is that you'll have an asymptomatic infection. – Mark Aug 10 at 21:37
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    Worth noting that this manufacturer has been tested (albeit not extensively) by the CDC and was found to have a filtration efficiency between 98% and 89%. – Geoffrey Aug 10 at 21:40
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In the US, in order for a mask to be labeled "medical", that mask must be approved by the FDA as a medical device. With so many new people manufacturing masks coupled with the public demand for masks, it is likely not profitable to delay to seek FDA approval. The FDA also is unlikely to approve a new manufacturer's mask without ASTM testing.

Thus, it is possible that these KN95 masks are a functional equivalent to N95 masks approved for medical use, but have not yet been approved by FDA.

Keep in mind that that coronavirus particles (fancy scientific name “virions”) are spheres with diameters of approximately 0.125 microns (125 nm). The smallest particles are 0.06 microns, and the largest are 0.14 microns. (Lancet)

The article here may be useful to help you sort through the efficiency of masks.

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    When reminding about the size of the virions, in comparison to the reference particle size for the masks, it should be mentioned that 0.3 is the size where the filters are the least efficient. Smaller particles, especially below 0.1 microns are filtered more efficiently due to the diffusion capture mechanism. Comparing with tests that used 0.007 micron particles is just pure nonsense. The filters do not act as a sieve. Cf., eg., Fig 4 in tsi.com/getmedia/4982cf03-ea99-4d0f-a660-42b24aedba14/… – Vladimir F Aug 10 at 10:19
  • In addition, KN95 masks don't seal as well as N95 masks, because they just loop around the ears rather than having multiple straps around the head: cdn.shopify.com/s/files/1/0075/2192/7257/files/… – Chris Aug 10 at 18:18
  • Note also that when the virus is expelled from the body, it rarely is alone. It's usually attached to some water or cells as it was expelled from a person's nose or mouth. Consequently, the effective size of the particles that need to be filtered are much larger that the size of the virus, >= 1 micron usatoday.com/story/news/factcheck/2020/06/11/… – Michael Altfield 10 hours ago
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Typically for an N95 mask to be considered "medical grade" it must be compatible with a sterile environment, such as by filtering both inhaled and exhaled air.

Surgical masks provide some filtration of exhaled air, which is why they're useful in surgury (e.g. keep saliva off an operating region). I have an N95 mask advertised for environments with dust and smoke (e.g. to wear while working with soil to prevent Legionnaires' disease). In these environments there's no need to filter air on the exhale; such filter would add to cost and increase the effort to exhale. For this reason "medical grade" N95 masks may be more expensive and more humid than those with a valve for exhaling air.

Unless there's a significant difference in how the filters are manufactured, then these masks are effectively the same for filtration of inhaled air. If medical grade masks were able to filter 99% of particles within a given size range then they would be N99 masks, not N95 masks.

However as @BobE mentioned "medical grade" likely must pass further tests and conform to other regulations (and perhaps requiring more expensive quality control measures) which would drive up the prices and could delay a product from reaching market.

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    Though a big point of wearing a mask against Covid-19 is filtration of exhaled air, to not infect others. – Paŭlo Ebermann Aug 11 at 21:57
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The mask protects people from the person wearing the mask. In surgery, my colleagues and I wear a mask to protect the patient's open wound from me. Do not make the mistake of thinking that you, as the mask wearer, are conferring a degree of protection that provides safety.

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