I was going to suggest the test tank that Flymen are producing, but Ard beat me to it.
I don't have one, but it appears to be a good tool if you're that serious about testing your flies before you hit the water looking for fish.
When it comes to designing your own patterns you will likely find that there is little that has not already generally been done. In that regard, most of our "new" designs are variations based on older patterns. Most anyone who has been tying for any length of time knows which materials they can or cannot substitute in patterns they may tie frequently, and that's often what new patterns amount to.
As far as flytire's opinion, I agree with him. However, some static testing can be advantageous for comparing materials & learning about the properties of those materials in water. How it acts in air will not be how it acts in water.
I used to test flies in my swimming pool in the warmer months, but that didn't provide an up close view. It was great for observing the action, although as flytire also said, did not allow for moving water situations. Although with streamers I could place them near the filter pump outlet & see somewhat how they would act in a current. That was of little value with topwater flies unfortunately. I miss having a swimming pool now!
Tying a section of tippet to a fly & viewing it in an aquarium can give you some ideas about material uses & comparisons between materials you substitute, so there is some value in it when it's the only method you have available.
To your question. Much of that knowledge only comes from tying experience & experimenting with different materials. There may be general knowledge in print or online, such as what Silver Creek said about substituting various materials for the wings in his example. This may not tell you how each material acts on it's own or for other purposes.
IMO, much can be learned simply by comparing materials visually. For example, fur such as opossum, rabbit & fox all have some similar properties, all being rather fine textured, but also have distinct properties. Each of course has different natural coloration, but that doesn't affect the movement of the hair. Color may be a consideration for why you might want to use each for a specific pattern. Opossum usually has more guard hairs and a distinctive shine to those hairs, while rabbit often lacks the number of guard hairs that Opossum has ( but not always, each animal is different). Fox is similar to rabbit, but has a different appearance to the underfur & is of course generally longer. You could however use any of these furs in a fly pattern with similar results, depending on the pattern type.
I substitute Badger fur for calftail in Crazy Charlie & similar patterns. I first learned that I could when I got some badger & compared the two materials visually. I had to remove the guard hairs in the Badger however. Turned out they both have similar motion when in water.
On many occasions I've looked at a new to me material & could see the potential in what I could tie with it, based on experience with similar materials. I may not have had a pattern in mind when I obtained the material. It wasn't until afterwards that I realized what it could be used for.
There are many materials with similar properties. The trick of course is learning what they may be & why you would choose one over another. The best way of course to do that is taking the time & expense to try different things & compare them for yourself.
You do have the advantage of the volumes of knowledge from forums such as this one. That can shorten the learning curse, er curve some. ( It might be a curse too at times! So many materials, so little time!
) But, there's never a substitute for first hand knowledge and that will require the investment of time.
The down side to all this is the time & cost of tying flies that may not prove productive. In my early years of tying I had many. Not so much now. Now, when I attempt to tie something "new" I have confidence it will catch some fish. That's the difference in all the years it took me to get this far & I'm sure others have experienced the same.
Just my 2 cents.
