Clear Jel is the thickener recommended for fruit fillings. Because it will get processed it will never have a firm texture. Cut the rhubarb into short pieces to reduce the length/size of the fiberous material. Strawberries obviously go will with this too.

The pH of rhubarb is lower than apples and way lower than blackberries, so if you wanted to give it a shot you could safely use either of those recipes for pie filling.

I'm just not sure how it will be texture-wise. If you try it let us know how it turns out.

Carol

Here is a link that might be useful: Apple Pie Filling

Actually, when you come to the bottom line, the Clear Jel may not be appropriate, as the higher acidic level of rhubarb will make the starch become seperated and loosen. National Starch company has several other starch options that hold up better to high acid foods. I forget the type they make specifically for this, but they even have some that hold up to repeated freezings too. There is a more stable starch called- Freezer Flow that has a better holding power compared to Clear Jel, and the Freezer Flo also works well with high acid foods. If you don't wish to thicken at canning time, but prefer to do it once opened, you may get a better texture that way.

Clear Jell should not break down. You will need to order the Clear Jell online ahead of time if you want to use it.
It isn't found in very many stores. A few county extension offices sell it, here Wilco, which is a feed and hardward store has it and one cake decorating shop does, too. It is cheaper for me to order online, even with the shipping.
You can do as mentioned and can the rhubarb plain with sugar and then thicken before you put in your pie.

Here is a link that might be useful: Canning rhubarb.

Guess there's nothing to do but give it a try! Still have some Clear Jel in the cupboard, so I'm all set. Thanks for all your advice.
SOS