Fold in half the end of the foam pad to be inserted first. Insert the foam pad into the cushion cover so that edge of the pad wrapped with batting goes in first and the side where the ends of the batting are exposed goes in last.
Slide the folded end of the foam pad into the slipcover.
Let the foam pad unfold so that it is sitting flat in the slipcover.
Use your hand to smooth down the batting.
Force a little more of the pad into the slipcover by squeezing and pushing in the pad and pulling up the slipcover (like wriggling into a tight pair of jeans). Use your hand to again smooth down the batting.
Continue pushing in a bit more of the pad at a time and smoothing down the batting until the pad is all the way in.
Use a wooden spatula to give the batting a final smoothing. The wooden spatula will allow you to reach all the way to the back of the cushion.
Pull gently on the two exposed ends of batting so that they are taut. Butt the two ends together to create a nice seam.
Zip up the cushion. Use the wooden spatula to make sure the batting stays tucked in as you zip.