The ones I got are comfortable enough, and they stay put. I love the feel of them.If it slips, feels bulky, or you can bite through it's a hinderance.
Some players who have jagged or irregular lower teeth suffer from irritation of the inner part of the lower lip that goes over the teeth. One of the common remedies is to cut a patch out of EZO denture cushions. When held under hot water the wax softens and the patch can be formed over the bottom teeth to make a soft cushion for the lip to sit on.BTW I've seen a couple of players with some sort of white plastic slip that they put in their mouth over their bottom teeth, so I guess it sits between their teeth and their bottom lip. I don't need one, my bottom lip rarely suffers even after a 3 hour band practice, but what are they for??
Kölbl (that's an o with an umlaut in the middle, if it doesn't display correctly.Thomann have them as well (but only in white and black at the moment). They're listed on the english language site as mouthpiece cushions...Try reeds direct and ask them for the 0.4mm clear ones made by KLOBL (unsure of spelling).
These are the best I can find by a mile.
That's the puppies!!!!!!