The panels should provide a cushioning layer between the tree and the horse. They can be made of leather or serge and filled with wool flock, foam or air. The following checks apply to all types.
Flocked leather panels will need a full reflock on a regular basis as the wool goes hard and lumpy over time. The regularity will depend on use but could be 1- 4 years. If the flock is less than 6 months old then more flock can be added but if older then a full reflock (remove and refill) is required as the flock beds down at a different rate and lumps willl form. It's important to check a saddle a few weeks after a full reflock so the flock has bedded down and any gaps/ lumps can be corrected.
A serge flocked panel will require regulating on a regular basis. This process evens out the flock and stops it compacting so it shouldn't require a full reflock.
Foam panels are low maintenance but eventually will go hard and need replacing.
Run your hand under the panels to feel for lumps.
If there are lumps then consult your saddler to clean up the tree.
Check the width of gullet. You should be able to run 3 fingers all the way along. It must not touch the bony spinous processes of the horse's back.
Run your hands along the panels with even pressure.
Are there gaps or lumps?
Are they hard?
Are they evenly filled?
Here is an example of what can lurk under the panels:
Note the layer upon layer of leather/ webbing, particularly bad through the middle and the D rings at the front and back. Also screws sticking out!
Flocking will not stop the horse from feeling the lumps - think wearing an extra layer of socks if you have a stone in your shoe! The lumps through the middle exacerbate the fulcrum effects of the curved tree, creating even more pressure.
Here is an example of how the tree should be dressed - no lumps!