An envelope cushion cover is a front panel and two back panels that overlap in the middle, so the insert slides in through the gap and no zip is needed. Cut the front 1 cm (3/8 in) smaller than the insert plus seam allowances, hem one long edge of each back panel, layer the backs over the front with the hems overlapping by about 7.5 cm (3 in), sew around all four sides and turn. It takes under an hour and is one of the best first projects for practicing straight seams and corners.
What size should a cushion cover be for your insert?
Make the finished cover 1 cm smaller than the insert in each direction. The insert then fills the corners and the cover looks plump rather than baggy. With a 1.5 cm (5/8 in) seam allowance on each side, the cut front is 2 cm (3/4 in) larger than the insert.
| Insert | Finished cover | Cut front |
|---|---|---|
| 40 × 40 cm (16 × 16 in) | 39 × 39 cm | 42 × 42 cm (16 1/2 in) |
| 45 × 45 cm (18 × 18 in) | 44 × 44 cm | 47 × 47 cm (18 1/2 in) |
| 50 × 50 cm (20 × 20 in) | 49 × 49 cm | 52 × 52 cm (20 1/2 in) |
| 60 × 60 cm (24 × 24 in) | 59 × 59 cm | 62 × 62 cm (24 3/8 in) |
| 30 × 50 cm (12 × 20 in) | 29 × 49 cm | 32 × 52 cm (12 5/8 × 20 1/2 in) |
Feather inserts compress more than polyester ones; with feather, you can go another centimeter smaller.
How big are the two back panels?
The top back panel covers 62 % of the cover's height and the bottom panel 55 %, which leaves an overlap of about 17 % of the height: enough to hide the insert without gaping. Each panel has a 1.5 cm seam allowance on three sides and a 3 cm (1 1/4 in) hem allowance on the opening edge.
For a 45 cm (18 in) insert:
- Front: 47 × 47 cm (18 1/2 × 18 1/2 in).
- Back top: 47 × 31.8 cm (18 1/2 × 12 1/2 in).
- Back bottom: 47 × 28.7 cm (18 1/2 × 11 1/4 in).
Which fabric, and how much?
Linen, cotton canvas, velvet, upholstery fabric and quilting cotton all work. Canvas and upholstery fabrics wear best on a sofa; linen softens beautifully with washing; velvet has a nap, so cut all the pieces with the pile running the same way, usually down.
For one 45 cm cover, you need about 50 cm (5/8 yd) of 150 cm (60 in) fabric, where all three pieces fit side by side, or about 80 cm (7/8 yd) of 110 or 140 cm (45 or 55 in) fabric. Two covers fit in about 80 cm of 150 cm fabric. The back panels can come from a contrasting fabric, which is a good way to use remnants.
How do you sew an envelope cushion cover?
- Prewash and press. Linen and cotton shrink, and a cover you cannot wash is a cover you will not use. The prewashing guide covers each fiber.
- Cut the three pieces on grain, centering any motif on the front.
- Hem the opening edges. On each back panel, press 1 cm (3/8 in) to the wrong side along the opening edge, then 2 cm (3/4 in), and stitch close to the fold. A second row of topstitching makes a neat detail.
- Layer. Lay the front right side up. Place the back top right side down, its raw edge level with the top of the front, then the back bottom right side down, level with the bottom and overlapping the first.
- Sew around all four sides with a 1.5 cm seam, pivoting at the corners with the needle down. Backstitch over the overlap, where the cover takes strain each time you change the insert.
- Clip the corners diagonally, 3 mm (1/8 in) from the stitching, and zigzag or serge the raw edges.
- Turn through the opening, push the corners out with a point turner or a chopstick, and press.
The straight seam guide covers keeping an even seam allowance and pivoting neatly.
How do you get sharp corners that do not look pointy?
Square covers often end up with "dog ears": corners that stick out once the cover is filled. Before sewing, taper each corner of the front slightly. Mark a point about 1 cm (3/8 in) in from the corner along the diagonal and blend it into the stitching line about 10 cm (4 in) away on both sides, then trim the back panels to match. The filled cover then looks square.
Envelope or zip, and can you add piping?
An envelope back is quicker and needs no notion; a zip gives a neater back and a firmer fit. For a zipped cover, the zip is about 5 cm (2 in) shorter than the cover is wide: a 40 cm (16 in) zip for a 45 cm cushion. To add piping, baste purchased piping around the front's seamline before you layer the backs, clipping its allowance at the corners, and sew with a zipper foot so the needle runs close to the cord.
Sewly's cushion cover pattern takes your insert size and gives the envelope or zipped version as cutting dimensions, since every piece is a rectangle and there is no point in printing them.