Don't overlook ribbon that you would source from a fabric store. Wider, heavier and stiffer.
Seems to be plenty of options on Amazon. Might want to waterproof them which will only make them heavier and stiffer.

 

None. Spend a little more and buy real sail tail, tails. For Sale - Sail tails

Bill

 

I’m just building cheap flags made from plastic bottles. Sail tails would be a little too nice for these and maybe too heavy.

 

I want to be able to see the flutter of a light tail, for me even the survey tape on a stick will indicate a condition change whereas heavier wont so well.

 

Try some spray starch on ribbon, both available at WALMART. The starch will make the ribbon/tails heavier, but just do light coats until you're happy.

 

I replaced my engineer tape tails with 100% polyester "decorative trim" ribbon, 2 inches wide by 4 yards per spool. Neon pink, neon yellow, purple...lots of color choices at Hobby Lobby or Michael's (just ask your wife - she'll know). Cut edges can be easily sealed from unraveling with a match, lighter, soldering iron, etc. Heavier than engineer tape but give good movement in slight winds.

 

My experience with plastic bottle wind flags is that surveyor tape is best. When using heavier materials it is easy to over balance the system. You can add a binder clip to the tail tame them a bit.

They are fragile though, you are correct.

Here is a video i did with them a couple years ago.