Masks don't make you rebreathe all your air: a simple at home experiment

Masks don't make you rebreathe all your expired carbon dioxided air.* The air you breathe out comes out the sides and top and bottom in a typical mask because this is the path of least resistance. This is why glasses fog when you wear a mask: because it's directing your humidified expired air straight up into your glasses instead of in front of you. Masks with a good seal across the bridge of the nose still let air out the sides and bottom. Masks with a good seal all around like an N95 let out the air directly through the mask material (or a valve, if your mask has one). This is because you inhale and exhale a higher volume than is in that little dead space between the mask and your face.

This would probably be better done with a TikTok or something but the only thing worse than taking selfies of myself would be taking a video of myself, so here's a blog post instead. If someone sees this and wants to video themselves doing this with their more beautiful face please do.

Anyway, here's the best picture in this whole post, of the supplies that are getting some nice, natural light coming through the window:

So first I exhaled as normally as possible into a sandwich sized ziplock bag. It's hard to breathe normally when you're thinking about breathing, and it's really easy to try to blow up your bag like a balloon. I chose a ziplock instead of a balloon because they have very low resistance to being filled with air, unlike balloons which require a bit of force to stretch. I didn't want to breathe through a straw and affect the flow of exhaled air that way, so I unzipped a small area in the corner of the bag and sealed my mouth under the overhang above the zipper. I wanted to underestimate how much I was exhaling rather than overestimate.

So here's my beautiful face doing that:

Here's the bag completely deflated to start:

Here it is inflated by one exhale:

It doesn't look very inflated and it isn't! But it does have air in it:

Then I folded the baggie to try to fit its entire volume fit under the mask, like what would happen if all your air got trapped behind it:

So here's what that looks like:

It's hard to even fit the whole bag behind the mask. And here's what wearing a mask normally looks like, for comparison:

And here's with my cloth mask, which is a little bigger, but still has parts-of-the-bag-sticking-out-the-sides problem. And the lower ties are much looser than how I usually wear them, with the edge of the mask in front of my chin instead of tucked slightly under it:

And here I am wearing it normally, without an actually-suffocating bag of plastic in the way. I even got to tie the lower ties tighter without the bag in the way:

Anyway, I promise that when you inhale/exhale you're exchanging air from around the outside of your mask.

*Inhaled AND exhaled air is actually mostly nitrogen, and exhaled air is still 16% oxygen, which is why you actually can breathe your own exhaled air for a short time, and why mouth to mouth resuscitation provides oxygen during CPR. But this is a tangent.