From The Tree Up - Panels (the Basics)

After you've looked at tree width, scoop and type, the next consideration would be the panels.  In this entry, I'm going to cover the basics, and explain panel modifications (and the conformations that need them) in a later post.

Basically, there are two main types of panels:  gusseted (which are almost always wool-flocked):

and plain panels (which are often but not always foam flocked):

The function of the gusset is to flatten and broaden the weight bearing surface in the rear of the panel.  This is a good thing for a broad-backed horse, but often not such a great thing for a roof-backed horse.  To illustrate, here's a photo of a broad-backed horse and non-gusseted panels:

The angle of the back is marked in green, and the angle of the panels is in red.  You'll notice that when the saddle is placed on the horse's back, the outer edge of the panel will make contact, while the inner edge will bear little to no weight.  Yes, it will squish down some when the rider's up, but not much, and the rider's weight will be concentrated in a fairly small area on the outer edge of the panel rather than being distributed over the whole surface.

Now, here' the same horse with a gusseted, flatter panel:

As you can see, the angles are much more agreeable with the gusseted panel, and there will be contact all along the weight bearing surface.

Now, to the other side of the fence.  Here's a roof-shaped back with a flat, gusseted panel:

In this case, the bulk of the weight will be borne on the inside of the panels, along the channel close to the spine, while the outer edges of the panels bear little to no weight.

Here's that same back with that more angled panel:

Again, the angles are far better, and you'd have panel contact over the entire surface.

Final word about panel basics:  adequate clearance in the channel.  The saddles shown above offer generous clearance for the spine, which will keep the rider's weight from resting on the spinous process.  And while you don't want to get too much clearance (too wide a channel will result in lateral instability), you certainly don't want to go to the other extreme, either:

This saddle wouldn't even offer clearance for the skinny end of a 2"x4" ... NOT something I'd recommend using on a horse.

Next up:  panel modifications, and the horses who need 'em.