Board building glossary

Foam and shape

EPS (expanded polystyrene): Foam made of fused polystyrene beads, light and cheap: the most common core for foil boards. It can only be laminated with epoxy, as polyester dissolves it.
XPS (extruded polystyrene): Closed-cell foam, denser and stiffer than EPS, that takes up very little water. It outgasses more: fit a vent plug and sand its smooth skin before laminating.
PU (polyurethane) foam: The traditional surfboard foam, easy to plane and compatible with both polyester and epoxy. Heavier than EPS.
Foam density: Mass of the foam per cubic metre (kg/m³). Board EPS ranges from about 15 to 30 kg/m³: denser foam resists dents better but weighs more.
Blank: The foam block the board is cut from. A “pre-shaped” or “CNC” blank has already been machined to shape from a 3D file.
CNC machining: The blank is milled by a computer-controlled machine from the 3D shape file: perfect symmetry and accurate concaves, with no hand-shaping skills needed.
Shape: The form of the board (outline, rocker, thickness, rails, bottom) and, by extension, the work of carving it. The shaper designs or carves it.
Rocker: The curve of the board seen from the side, nose to tail. More nose rocker avoids pearling; a flat rocker helps the board get going sooner.
Concave: A hollow shaped into the bottom of the board (single, double or triple concave, V) that channels the water: easier take-off and softer touch-downs.
Rails (edges): The edges of the board. Their shape (round, hard, chined) changes how the board releases water. Not to be confused with the US rails of the foil box.
Stringer: A wooden strip glued down the middle of the blank, nose to tail, that stiffens classic surfboards. Sandwich foil boards usually do without one.

Cloth

Glass cloth (fibreglass): Cloth made of glass fibres, the most common in home building: cheap, easy to wet out, and clear under resin. Less stiff than carbon for the same weight, but more forgiving to impacts.
Carbon cloth: Cloth made of carbon fibres, very stiff and light for its strength. Dearer than glass and less forgiving to point impacts: it is often combined with glass.
Hybrid lamination: Carbon and glass layers combined: carbon brings stiffness, glass brings impact resistance and a lower cost.
Fabric weight (areal weight): Mass of a cloth per square metre (g/m²). The higher it is, the thicker and stronger the skin, but the heavier. Foil boards commonly use 80 to 300 g/m² depending on the area. Read the guide →
Weave: twill and plain: How the fibres are woven. Twill drapes better over curves and gives the diagonal pattern; plain weave is more stable but stiffer.
Biaxial (±45°) cloth: Cloth with fibres at +45° and -45°, usually stitched rather than woven. It handles torsion well and drapes easily.
Unidirectional (UD): Cloth or tape with nearly all fibres in one direction: very stiff that way. Used for targeted reinforcements, under the feet, around the boxes or along the board.
Roll width: Width of a roll of cloth (for example 100 or 127 cm). It sets the length to buy: a board wider than the roll needs two pieces or a bias cut.

Resins and fillers

Epoxy resin: A two-part resin, resin and hardener, mixed at a precise ratio. It bonds very well, shrinks little and suits EPS: the standard for foil boards.
Polyester resin: The traditional surfboard resin, cured by a catalyst (MEKP). Cheap and easy to sand, but it dissolves EPS and XPS: for PU blanks only.
Hardener (slow, fast): The second part of epoxy. A slow hardener leaves more working time, a fast one speeds up the cure. For a first board, slow avoids working in a rush.
Catalyst (MEKP): The hardener of polyester resin, added in small amounts (often 1 to 2%, per the data sheet). Corrosive: gloves and glasses required.
Mix ratio: The resin / hardener proportion set by the maker, for example 100:30 by weight. It is not adjustable: weigh to the gram, a wrong dose stops the resin curing properly.
Pot life: How long the mix stays fluid enough to work. It gets shorter with heat and with the amount mixed: several small batches beat one big one.
Exotherm: The heat given off by curing resin. In a cup it can run away (smoke, foaming resin); on the board, too much heat makes the foam outgas.
Cure and post-cure: Curing is the hardening of the resin, from a few hours to several days depending on temperature. A post-cure, gentle controlled heating, then improves heat resistance.
Amine blush: A greasy film that forms on some epoxies curing in damp or cold air. It stops the next coat bonding: wash it off with water before sanding. A peel ply avoids it.
Microballoons: Hollow microspheres added to resin to make a light filler that sands easily: filling, blending, fillets. Read the guide →
Fumed silica: A very fine powder that thickens resin so it does not run (thixotropy): glue for boxes and PVC, paste on vertical surfaces. Read the guide →
Milled fibre: Very short glass or carbon fibres mixed into resin to make a structural glue, for example around the boxes. Read the guide →
Fill coat: A coat of resin applied after lamination to fill the weave of the cloth, then sanded to a smooth surface before the finish. Read the guide →

Vacuum bagging

Vacuum bagging: Pulling the air out from under a bag while the resin cures: atmospheric pressure compacts the lamination and removes excess resin. For EPS, a moderate vacuum is enough (about -0.2 bar). Read the guide →
Wet lay-up (hand lay-up): Laminating by hand with a brush and squeegee, without vacuum: less equipment, but a little more resin in the cloth, so a little more weight.
Peel ply: A cloth laid on the fresh lamination and peeled off once cured: it leaves a clean, matt surface ready for the next coat without sanding.
Perforated release film: A plastic film with small holes, laid over the peel ply under vacuum: it lets excess resin through to the breather without sticking.
Breather: A felt laid under the bag: it soaks up excess resin and lets the air flow to the valve, so the vacuum reaches everywhere.
Vacuum bag: An airtight film wrapped around the board. Sealed with sealant tape and connected to the pump through a valve, it presses onto the board as the air is pulled out.
Sealant tape (tacky tape): A sticky bead that seals the vacuum bag airtight, and peels off afterwards.
Vacuum pump: A pump that draws the air out of the bag, with a gauge to read the vacuum level. A rotary vane pump does the job; a modified aquarium pump can work on a small budget. Read the guide →

Build and reinforcements

Sandwich construction: A rigid foam (PVC) between two skins of cloth: spacing the skins multiplies stiffness for little weight and spreads impacts. Partial, deck only or full depending on the areas covered. Read the guide →
Monolithic build: Lamination laid straight onto the foam, with no PVC sandwich: simpler and cheaper, but less resistant to heel dents.
High-density PVC foam (Airex, Divinycell…): A rigid closed-cell PVC foam, much denser than EPS. It is used as sandwich core under the lamination, as the plate for the boxes and as blocks for the inserts: it spreads loads and resists crushing.
Lamination: Covering the foam with layers of cloth wetted with resin, which form the board’s stiff skin. The “lamination schedule” says which cloths go where, and how many layers. Read the guide →
Outgassing: Air coming out of the foam as it warms up, making bubbles under the fresh lamination. Limit it by laminating while the temperature drops, then manage it with a vent plug.

Boxes and fittings

US box (US rails): A pair of parallel rails set into the board, into which the foil mast plate is bolted with sliding nuts. The wingfoil standard: it lets you move the foil forward or back.
Tuttle and Deep Tuttle: A deep box the mast head (or a fin) slides into, held by two screws through the deck. The longer Deep Tuttle is common in windfoil and surf foil.
Mounting plate: A block of high-density PVC (home-made or sold ready to fit) that holds the US boxes and spreads the loads from the mast through the board.
Inserts: Threaded sockets set into the board to screw on footstraps, the handle or the leash plug. They are glued into high-density PVC blocks so they do not pull out.
Vent plug: A small valve with a breathable membrane (Gore-Tex type): it lets air out of the foam when the board heats up in the sun, without letting water in. A must with EPS and XPS.
Deck pad (grip): EVA foam glued onto the deck for grip and foot comfort.

Tools and safety

Trim router: A small one-handed router. With a bearing bit and a template, it cleanly cuts the pockets for the boxes and inserts.
Template: An MDF or plywood pattern that guides the cut or the router: board outline, box pocket, rocker profile.
Squeegee: A flexible spreader that works resin into the cloth and pushes out excess resin and air bubbles.
Protective gear (PPE): Nitrile gloves and glasses whenever you handle resin, covering clothes, an FFP3 mask against sanding dust and a cartridge mask (A2P3) against fumes. Once you develop an epoxy allergy, it is for life.

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