It's made of an extreme shock-absorbing material, so any movement from you or your saddle is being absorbed by the saddle pad instead of your horse's back.
Jumper12 - My saddle was a little too wide for her, and she's still growing - so I got their saddle pad that comes with inserts. Last year I used the inserts to complete the fit, then took them out this year because she grew into her saddle. I wouldn't recommend using this pad if your saddle is too tight, there's not really a fix for any saddle that's too tight. It's kindof like wearing a shoe that's too tight, wearing a different sock isn't going to help, it will probably just make it worst if that makes sense?