It sounds like a puzzle: a 20-inch pillow insert, an 18-inch cover, and a zipper opening that is shorter than both. The answer is to fold the soft insert before it goes in. Once it is through the opening, you can unfold it and settle it into the corners. The cover and zipper should never need a hard pull.
Why use an insert larger than the cover?
A slightly larger insert fills out the corners and gives a decorative pillow a fuller shape. It is a styling choice, not a requirement for every pillow. For that full, styled look, a 20-inch insert in an 18-inch square cover is a good place to start.
This fold-and-insert method works with our square covers in soft spun polyester, cotton canvas, and cotton linen. The feel of the insert matters too: a soft insert compresses through the opening and expands inside the cover. If an insert is very firm or heavily filled, take your time and let the cover and zipper tell you if the fit is too tight.
How to put a 20-inch insert into an 18-inch square cover
Even if the zipper opening is only about 13 inches, the soft insert goes through folded, not flat. The same method works when you choose a 22-inch insert for a 20-inch square cover.
- Open the zipper all the way. Lay the empty cover flat, with the opening facing you. Check that the zipper is fully open before you begin.
- Fold the insert in half. Bring two opposite sides together so the insert makes a soft taco shape. Hold that fold while you guide it in.
- Ease the folded insert through the opening. Feed one folded end in first. Hold the cover near the opening and work the fabric over the insert a little at a time. Compress the insert with your hands; avoid pulling on the zipper or seams.
- Unfold it inside the cover. Reach in and gently guide the insert into the two far corners, then the corners by the opening. Pat the pillow until the filling sits evenly.
- Move the filling away from the zipper and close it slowly. Bring the two sides of the cover together before pulling the zipper. If fabric or the insert catches, back up, free it, and try again. Finish by fluffing the pillow.
That folded method is also shown in Room & Board’s pillow instructions. The important detail is to settle the insert away from the opening before you zip.
What if the opening still looks too small?
The insert does not have to pass through at its full 20-inch width. A soft insert narrows when folded. Go slowly, especially where the zipper ends meet the seams. If the folded insert will not go through without force, stop. A softer insert or one that matches the cover size is the better choice.
How do I know if the insert is too full?
After you have unfolded and settled it, look at the cover. The fabric should look full without seams pulling apart, corners distorting, or the zipper bowing outward. You should be able to bring the zipper edges together with your fingers and close it without fighting the pillow. If you cannot, try a less firmly filled insert or a smaller size.
Do I have to size up?
No. An insert that matches the cover size gives a softer, more relaxed look and is usually easier to put in. For a fuller look, an insert up to two inches larger is a useful starting point for many square covers. Choose the look you like, and let the feel of the fabric and insert guide the final fit.
Looking for a cover to refresh a sofa or reading corner? Explore our throw pillows and covers, and check each listing for its size, fabric, and whether an insert is included.