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I've been wearing BTE (behind the ear) hearing aids since I was a kid. So I have the custom molded ear plugs (with hole for tubing) like you mention. I enjoy that they're a magical always-ready pair of earplugs. But recently trying to use some actual ear plugs to help sleep at a noisy location... I thought they weren't helping, and then I learned from my wife that I wasn't using them correctly. It seems the trick was…
From using regular ear plugs, my experience is that you really need to get them in there quite far. Also, I find that the disposable ones are really basically single use. After they've compressed and expanded I find they don't seem to work as well on subsequent uses. So, taking them out and putting them back in is something I would try to minimize. Maybe they've improved in the meantime? The molded plugs to me do fee…
With (high power) hearing aids, it's reasonably easy to know if you have a gap in the mold: I'll get a feedback loop (annoying noise, naturally) if one is loose or a poor fit. Interestingly, for the past few molds (a 4-6 year life per pair these days) the left ear definitely has more of a problem with feedback loops when my jaw is opened wide (i.e. eating) - the shape evidently varies more with this movement than the right ear does.