Yes, soft Is much better. Earplugs are soft. The thing is, when you move, the opening of the canal changes slightly in size and shape allowing sound to get out. You need something soft and flexible to fill that. If you look at Amazon you can see earplugs are sold that you make yourself just like a hard one the audiologists make. The one reviewer made the same point that they aren’t as good as a soft flexible plug.
But also, the way I do it — with much trial and error — is to get the tube pointed directly at my wife’s eardrum. The audiologist was never able to do that right. As soon as I started making these ear molds, in addition to eliminating the feedback, my wife said she could hear much better.
I should emphasize it’s a complicated time-consuming process for me. And I may use sections from up to five different earplugs. But with my wife’s hearing loss is severe as it is, it’s worth the trouble.