Was interested to find this thread; just thought I'd add a bit of own past 'experience'..
Right back when I used to have a schoolmate with whom I had some fairly serious tie-up games, we found (pretty much by accident) that layered scarves made very secure & silencing gags even without mouthstuffing.
By alternating first a wool scarf (doubled), folded silk scarf & the same again till 3 of each were applied, the top 4 going over the nose as well, it was enough to make breathing a bit harder, but not difficult.. Occasionally, a mouthstuffing was used as well.. we had an old wool blanket that we used to cut 4"-5" squares out of...Very absorbent, strange sensation to be gagged with & used to taste a bit interesting after an hour or more..But sometimes almost better than the school food..!!
We got it to incorporating reversed balaclavas as well, & topping it with folded heavy sweaters, which all used to make it get quite warm under that lot too... Sometimes layered gags with a parka worn backwards & hood up over face was another good arrangement..
When I reached the stage of doing it with my wife, she caught on to the idea very fast too, & by this time, we'd found ALL sorts of 'useful' things available that work well as layering gags; including big long satin wraps, heavy alpaca or mohair shawls, faux fur scarves & snoods, (have also used vintage stoles as well..they 'work' just on their own..!!

).. & now, thick soft nylon down scarves as well.. ( All stuff that can be kept around, looking pretty 'innocent' as well..!!!

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