There are two straight-of-grains in fabric. WOF is width-of-fabric, and is how most of us cut strips for piecing and also for binding. The cut extends from one selvedge edge to the other. This is the most stretchy straight-of-grain. This is probably how you cut your strips. If your pad's corners are round (say, the size of a small saucer), then this cut will probably not have enough stretch in it to get around the corners. If the corners are more softly rounded (say, the size of a dinner plate) then there may be enough stretch in this cut.
The most stable grain runs the length of the fabric (parallel to the selvedge). When possible, quilters like to cut border strips with this grain because it makes the borders more stable.
Bias is anything that is cut off-grain. The stretchiest bias is cut 45 degrees to both straight-of-grains. Bias strips cut at different angles will still be very stretchy, but the closer you get to the straight-of-grain on one edge or the other the less stretch the strip will have.
You can test all these with your fabric. Hole your hands 8 inches or so apart and grab your fabric in each hand. Pull. On the lengthwise grain you will see little or no stretch. On the crosswise grain you will see a little stretch. On the bias you will see a lot of stretch.