Fabric tail help

So I went and got some paper to trace out tails for me and my Mersibling I want to just make tester tails I don't want to spend a whole bunch of time and money making a tail to test out and not like so I just want to make plain simple tester tails but my question is when making a fabric tail does it have to be spandex or swimsuit fabric like can you use a different fabric that is kind of similar I have black swimsuit fabric but I don't have enough to make two tails I myself am a plus size person and I'm also 5 foot 11 my sibling is 9 not very big and not very tall so I want to use the swimsuit fabric for him the fabric I want to use feels like swimsuit fabric but it's not I just want to know if you have to use spandex or something Fabric or is it safe to use other Fabrics I have all day and tonight to make them if I want to make them in time to go to the Springs tomorrow and if I can't make them then I will do it next time any advice is more than welcome.
thank you

most of my fabric tails I made with crushed velvet.

I use medium to heavy weight spandex.