Is there a mouthguard that blocks mouth-breathing?

The Good Morning Snore Solution blocks mouth breathing. You can still open wide and take a breath if you need to, but in normal use it completely seals off your mouth. As a bonus, it was by far the most effective oral appliance I tried for apnea before accepting that I needed CPAP. It holds the tongue forward, which really made a difference for me. Devices that hold the lower jaw forward helped very little. It may even help further reduce your AHI with CPAP.

The material is very thin. I found it to be more comfortable than the competing design sold on Amazon under various names.

The catches?
1) You must breath through your nose, so the sinuses must be clear. As I said, you can open wide and take a breath, but ....
2) If you can curl your tongue (some people can, some can’t), you can easily slide ride out of it.

I had trouble keeping it in all night. The newer young adult size is a little more snug, but doesn’t solve the tongue curl problem.

here is what i've been playing with for the last week or so. it's the plastic film that covers a tub of Brummel & Brown (Made with Real Yogurt) margarine type spread. cutting it in half gives me the right fit for my mouth.

fits between front teeth and inside of lips. i have a slight under bite. and some nights i can't get jay's scunci rig to hit just so to prevent a bit of my lip being sucked in that gap. not the end of the world, but a bit bothersome. this plastic film helps solve that.

and i don't have to pay anything for it as it's part of what we already buy.

oh be still my cheap ass heart!