Towel is also two types one is bath towels which is special weave to form loops to give extra absorbing capacity n other one is plain weave towels normally used for cleaning purpose like kitchen towels etc. Poplin isn’t even slightly like flannel. Poplin is very tightly woven, smooth, shiny and used for a lot of different types of clothing from jackets to pyjamas to shirts. Flannel is more loosely woven and is never smooth or shiny. It has to be super soft. It’s brushed to create the We Stand With State Spartan Strong Hot 2023 Shirt But I will love this napped surface on either one side or both sides. Both cotton and flannel are breathable. But the napping process responsible for flannel fuzzy texture also traps warm air .so although flannel is more loosely woven than cotton, it’s also naturally warmer . It should, but I would suppose that it depends on the felt, the flannel, and the angle that you require it to adhere. At best, it will be a weak bond, that would not survive a strong wind or handling. If you want to use a flannel cover for a layout board or wall, as for a quilt project, that is possible, but I would worry about the weight of the felt. Felt is dense and thick, which makes it heavy. Quilting cotton stays on a quilt wall mostly because it’s light and made of a natural high friction fiber. Wool is also high friction, but is much more weighty when felted. If I were planning to use felt, I would use it as the wall, and I would anchor the bottom of the wall about a foot forward of the top. That would create enough slope to ensure that none of the flannel pieces slide down.