Planning a Window Seat or Bench Cushion: Foam, Fabric & Cover Guide

A window seat is the piece of furniture people love most and think about least. Get the foam, fabric and cover right and it becomes the reading spot of the house; get it wrong and it is a hard, faded plank with a cushion that slides off. Here is how to plan it properly, from measuring to the last zip.

Start with how it will be used

Be honest about the job. A hall bench you perch on to put shoes on needs 50 mm of firm foam and a hard-wearing fabric. A bay-window seat you will lie in for an hour with a book wants 75–100 mm and something soft against the skin. A kitchen banquette that the kids eat at every day wants a performance fabric with a wipe-clean finish. The answer to almost every question below comes from this.

Measuring the seat

1. Measure the length at the front and the back – window bays are rarely square. Take the smaller and note the difference.
2. Measure the depth at both ends and the middle. Anything over 600 mm deep is a day bed; anything under 400 mm is a perch.
3. Note any angles in a bay window. Make a full-size cardboard template of the seat top; it is the only reliable way.
4. Check the clearance under the sill. A 100 mm cushion plus a 20 mm wrap on a seat 40 mm below the sill will push into the window.
5. Decide whether the cushion should sit flush with the front edge or overhang by 10–15 mm for a softer look.

Subtract 5 mm from the length and depth so the finished cushion drops in without forcing, then add the foam oversize (below) when you order.

Choosing the foam

Use	Thickness	Density
Hallway or entry bench	50 mm	HR35 firm
Kitchen banquette	50–75 mm	HR35
Bay window reading seat	75–100 mm	HR35 with 25 mm soft top
Window seat doubling as guest bed	100 mm	HR35

High-resilience 35 kg/m³ foam keeps its shape under daily use; anything softer sags at the front edge within a year on a fixed timber base. Our HR35 sheet is 2000 × 1000 mm, which covers most window seats in one piece; longer seats are joined with spray adhesive along a vertical seam. Order foam 10 mm longer and deeper than the finished cover so it fills the corners, and match the thickness to the boxing height.

Wrap the foam in 200 gsm Dacron across the top, front and bottom. It softens the edge, hides the foam outline and lets the cover slide on. For bench cushions that get moved a lot, a thin non-slip mesh under the cushion stops it walking off the seat.

Choosing the fabric

Window seats live in the sun, so the fabric rules are closer to outdoor than lounge. In NZ light a north-facing seat sees UV that would fade an ordinary cotton print in two summers.

• Sun-exposed seats: solution-dyed acrylic or a performance polyester with a lightfastness rating of 5+. Our Coastal outdoor canvas is colourfast, water-repellent and feels like a cotton canvas.
• Family kitchens: a stain-resistant performance weave, 40k+ Martindale, W-S cleaning code – for example Sentinel performance weave.
• Formal rooms out of direct sun: linen or a linen-look weave gives the classic soft look; velvet works if the seat is not in the sun.
• Avoid: pile fabrics on a seat people slide along, and light cottons on a seat that faces the window.

Choosing between fabric families is covered in detail in our complete fabric buyer’s guide. Order swatches before committing; a colour that looks cream in the shop can read yellow in west light.

How much fabric

A box cushion uses a top and bottom panel, a boxing strip round all four sides and a zip panel at the back. On 140 cm wide fabric:

• Seat 1200 × 450 × 75 mm: about 1.5 m
• Seat 1800 × 500 × 100 mm: about 2.2 m
• Seat 2400 × 550 × 100 mm: about 3 m (top panel will need a seam or railroaded fabric)
• Add 0.5 m for piping, and 15–20% for pattern matching on a print or stripe

For a bay window with three angled sections, treat each as a separate cushion – they fit better and can be turned to spread wear.

Designing the cover

• Zip: full-length along the back boxing, extending 100 mm round each corner, so the foam can be removed for washing.
• Piping: optional but it sharpens the edges and hides seam wear. Use a 4–5 mm cord and the same fabric or a contrast.
• Ties or Velcro: two or three short ties at the back keep the cushion from sliding on a smooth painted seat.
• Bottom panel: a cheaper, breathable fabric underneath saves money and lets the foam vent.
• Thread: bonded polyester, UV-resistant if the seat is in the sun.

Storage lids and hinged seats

Many window seats double as toy boxes or linen storage with a hinged lid. The cushion then needs to be fixed to the lid rather than loose, or it slides off every time you open it. Two options: stick Velcro strips along the front and back edges of the lid, or upholster the lid directly by stapling the cover to the underside with a 25–50 mm foam layer and wadding, the way you would a dining seat. Keep the total build-up under 60 mm so the lid still clears the sill and the hinges are not overloaded.

Buttoning and extras

Buttoned window seats look wonderful and hold the wrap in place, but buttoning through 100 mm of foam needs a long needle and strong twine. Keep buttons to the top panel only, at 200–250 mm spacing, and use covered buttons in the same fabric. If you want scatter cushions to match, buy an extra metre now; dye lots change.

Doing it yourself or ordering it made

A straight bench cushion is a satisfying weekend sewing job with a domestic machine and a zipper foot. Angled bay-window sets with piping and buttoning are a step up. Send your template and measurements through our contact page for cut foam and a metreage check, and if you are in Auckland and would rather have the whole seat made and fitted, our sister workshop Upholstery World makes window seats and banquettes on-site.