The best foam board for kinusaiga

The short answer

Use XPS (extruded polystyrene) insulation board, 3/4 to 1 in (19 to 25 mm) thick, from the insulation aisle of a hardware store. It is the pink, blue or green rigid panel builders put in walls. A 4 x 8 ft sheet gives you 72 boards of 8 x 8 in, at roughly 40 cents of foam per board.

Avoid the white foam made of little balls (EPS) and rubbery craft foam sheets. Paper-faced foam core from the dollar store works for small pieces but grips less. Everything else on this page explains why, and how to get the most out of your sheet.

Why XPS insulation foam is best

Kinusaiga asks three things of a board: that a knife cuts a clean, narrow slit in it, that the slit stays tight enough to pinch the fabric pushed into it, and that the surface stays flat and smooth under the fabric. Extruded polystyrene does all three.

• It is dense and uniform. XPS is made as one continuous closed-cell material, with no beads or grain. A sharp blade slices it like cold butter and leaves a clean groove with smooth walls.
• It springs back a little. The walls of the groove press gently on the fabric, which is what holds a tuck without glue.
• It is rigid and light. A 1 in board does not bend in your hands, does not warp with humidity, and weighs almost nothing once framed.
• It is cheap and easy to find. Every home improvement store stocks it all year.

The colour is just the brand. Pink is Owens Corning FOAMULAR, blue is the STYROFOAM brand (DuPont), and green is GreenGuard (Kingspan), which Lowe's carries in many areas. They are all XPS and they all work. Under thin white or pale fabric a strong pink or blue can show through slightly; an adhesive sheet or a layer of plain white cotton under the palest pieces fixes it.

Where to buy it and what it costs

Look in the insulation aisle (not the craft aisle) of Home Depot, Lowe's, Menards, Ace, or any lumber yard or builders' merchant. In Canada and the UK the same boards are sold by building suppliers, often under the same names. Ask for "rigid foam board insulation, XPS".

• 4 x 8 ft sheets (1.2 x 2.4 m) are the standard size, in thicknesses from 1/2 in to 2 in and more. At the time of writing a 1 in sheet costs roughly $25 to $35 in the US, depending on store, brand and region. That is 72 boards of 8 x 8 in, so about 35 to 50 cents per board.
• 2 x 8 ft sheets are stocked in some stores and fit in a car more easily.
• 2 x 2 ft project panels (60 x 60 cm), 1 in thick, are sold by some stores under the FOAMULAR name. One panel makes nine 8 x 8 in boards: the best option if you only want to try the craft.

A full sheet is light but big. If it doesn't fit in your car, cut it in half or in thirds in the parking lot: score a line deeply with a utility knife against a straight edge, then snap it over your knee or the edge of the tailgate. Some sheets are "scored" at the factory with shallow cut lines on one face to make snapping easier; check both faces before you plan your boards, and work on the smooth one.

Prefer not to deal with a big sheet at all? Pre-cut boards come in most kinusaiga kits and are sold in packs by Etsy sellers. You pay much more per board, but they arrive square and ready.

Which thickness to choose

Grooves only need to be about 1/8 in (3 mm) deep, up to 1/4 in (6 mm) for thick fabric, so depth is never the problem. Thickness is about stiffness and framing. Ordinary picture frames are too shallow for a 1 in board, so if you plan to frame, look at shadow-box frames before you buy foam. More in finishing and framing.

Every board compared

The other boards, one by one

EPS, the white bead foam: not recommended

Expanded polystyrene is the white foam used in packaging, cheap coolers and some insulation panels. Look closely and you will see it is made of little balls fused together. A knife tears between the balls instead of cutting through them, so the grooves come out ragged, the beads pop out as you push fabric in, and the white crumbs get everywhere. People often call it "Styrofoam", but STYROFOAM is actually the brand name of the blue XPS board, which is a different and much better material.

Foam core (paper-faced foam board): fine for small pieces

The poster board sold at Dollar Tree, office stores and craft shops is a thin sheet of foam between two layers of paper, usually 3/16 in (5 mm) thick. It works, and it is a reasonable way to try the craft for a dollar or two, but it has limits:

• You have to cut through the paper face, and the groove can only go a couple of millimetres deep, so it holds less fabric.
• The paper edges of the groove can fray and open up if you tuck the same spot several times.
• A large board bows, especially once fabric pulls on one face.

Use it for ornaments, coasters, cards and patterns with large pieces in thin cotton. Thicker foam board (3/8 or 1/2 in) from art suppliers behaves better, but at that price XPS is cheaper and grips more.

EVA craft foam: no

The soft, colourful foam sheets used for kids' crafts are only about 2 mm thick and rubbery. A cut closes up behind the blade and there is no depth to hold anything. Leave them for other projects.

Wood and cork: the traditional way

Traditional kinusaiga in Japan is made on a wooden panel with carved grooves, with glue to hold the silk, and kimekomi dolls are carved from wood or moulded from a sawdust paste. It is beautiful and permanent, but carving grooves in wood takes chisels and patience, and mistakes cannot be undone. Cork is easier to cut but crumbles at the edges of a groove and is too thin in most craft rolls. Start with foam; see kinusaiga vs kimekomi for the traditional side.

Pre-cut kinusaiga boards

Kits and Etsy shops sell boards already cut to size, sometimes with the pattern printed on them or even pre-scored. They are handy for gifts and workshops and save you buying a whole sheet. Check what the board is made of (it should be XPS or dense foam, at least 1/2 in thick) and the size, since many are smaller than they look in photos.

How to cut a sheet into boards

A 4 x 8 ft sheet (48 x 96 in) divides exactly into 72 squares of 8 x 8 in (20 x 20 cm). Cut long strips first, then cut the strips into squares: it is faster and the squares come out truer.

1. Work on the floor or a big table, on an old sheet of cardboard so you don't score the surface below.
2. Mark the strip width at both ends of the sheet, then join the marks with a long straightedge: a metal ruler, a level or a drywall T-square.
3. Cut with a long, fresh blade: a snap-off utility knife with the blade extended. Make a first light pass to set the line, then several more passes, each a little deeper. Forcing one deep cut drifts off line and tears the foam.
4. Or use a fine-tooth saw. A drywall saw, a hacksaw blade or even a serrated bread knife goes through 1 to 2 in foam easily. Keep it upright and let the teeth do the work.
5. Cross-cut each strip into squares with a carpenter's square or a set square so the corners are true.
6. Clean the edges with a few strokes of fine sandpaper or a sanding block. Vacuum the crumbs: they cling to everything.

For boards up to about 3/4 in, score and snap is quicker: cut about a third of the way through along the ruler, put the line on the edge of the table and press down. The break is slightly rough, which does not matter if the edges are wrapped or framed.

Adhesive sheets

Many makers stick a double-sided adhesive sheet on the board before they start. It is optional, but it keeps each fabric flat while you tuck, stops large shapes from sagging, and hides the colour of the foam under pale fabric.

• What to buy: double-sided adhesive transfer sheets, such as 3M 468MP (sold in sheets and rolls), or generic double-sided craft adhesive sheets sold for card making and scrapbooking. Pick sheets at least as large as your board, or butt two sheets edge to edge.
• When: stick it on the bare board before scoring. Peel one liner, lay the sheet on the foam and smooth it from the centre outwards. Leave the top liner on.
• Then: tape the pattern over the liner and score straight through everything. As you work, peel the liner off one shape at a time, just before you lay its fabric.
• Mind the strength. Strong adhesives like 468MP grab fabric for good, so lower each piece carefully. A lighter, repositionable craft sheet is more forgiving if you like to adjust.

Board ready? Follow the step-by-step guide, see the full supplies list, and pick a free pattern: each one comes with true-scale cut maps for 8, 6 and 5 in boards.