Plumbers PTFE Pipe Sealant Tape, 5.5mil Thick, Flex Seal Tape Waterproof, -212 to 500 Degree F Temperature Range, White (1/2 by 520 Inches 1 Roll)

Sorry, didn't edit my Amazon links properly. Here's my comment again: I haven't found anything like that, but I think you could make this yourself with some felt, hand sewing, and a chopstick + the bendy bit inside. I'm assuming the bendy bit is aluminum ribbon; https://www.amazon.com/Mandala-Crafts-Aluminum-Sculpting-Gardening/dp/B07QMZJV95/ref=mp_s_a_1_1_sspa? I'd make a felt tube to specifications + like a quarter inch for seam, sew inside out. Flip right side in with a chopstick or a safety pin. Cut the aluminum ribbon to length (remember you have to close the tub so cut it a bit shorter than the tube) and wrap it in some of this to make sure it doesn't poke out of the felt: https://www.amazon.com/DOPKUSS-Plumbers-Sealant-Waterproof-Inches/dp/B095YCMHNX/ref=mp_s_a_1_1_sspa? And then stick that entire operation inside your tube. Alternatively you can just hand sew the tube around the metal ribbon and leave the whole thing inside out. You could also buy a big pack of pipe cleaners and use those instead, I'm just not sure they're durable enough for a cat toy. You get a yard of felt you can churn out like two dozen of these