Kevlar Fabric: Weights, Weaves and Why It Only Runs With Epoxy

Boat Suppliers

05 November 2026

Kevlar fabric is the reinforcement you spec when the failure you are designing against is impact and abrasion, not stiffness. Kevlar 49 aramid runs 1.44 g/cc against 2.54 for E-glass and 1.78 for carbon, it is tougher on impact than either, and it is roughly five times weaker in compression than in tension, which is why it is almost always a skin ply or a hybrid and almost never the whole laminate. Here is how to pick a weight and a weave, and why every one of them runs with epoxy.

What aramid does that glass and carbon do not

Hit a glass laminate hard and it cracks; hit carbon and it shatters; hit aramid and it dents, stretches and stays in one piece, because the fiber yields instead of breaking. Drag it over rock and it fuzzes rather than wearing through. That is the whole case for it: canoe and kayak hulls, skid plates, the inside face of a carbon panel that has to survive a strike, racing hull impact layers, kart and motorcycle bodywork. The bill for that toughness is real. Aramid fails early in compression by fiber buckling, at about a fifth of its tensile strength, so a beam or a panel that bends wants carbon or glass on the compression face. It absorbs moisture from the air, so cut edges and drilled holes get sealed. It cannot be sanded clean; it fuzzes, so you shape a Kevlar surface as little as possible and fair over it. And it degrades in sunlight: very thin aramid fabric in direct high-intensity sun can lose about half its tensile strength in days, so it always sits under gelcoat, paint, clear coat or a carbon face ply, never as the outer surface.

Weights: 1.7 oz and 5 oz

Two weights cover nearly every job. The 1.7 oz style 120 plain weave, Kevlar 49 at 195 denier and 34 x 34 ends per inch, is about 0.004 in (0.1 mm) per ply and tests around 200 lb/in dry breaking strength. It adds an abrasion and impact skin without adding weight you can feel, which is why it shows up as the inside ply on carbon panels and the outer ply on lightweight paddle craft. The 5 oz plain weave, industry style 281 at 1140 denier and 17 x 17, is about 0.010 in (0.25 mm) per ply and is the structural canoe and skid plate weight; the 4-harness satin version, style 285, is the same yarn in a weave that drapes over a stem. Anything heavier is specialty ballistic or industrial cloth and is the wrong material for a laminate.

Weaves and hybrids

Plain weave is stable on the table, holds its shape while you wet it out, and bridges a tight radius. 2x2 twill shears and follows a curve. Satin drapes best of all and is the least stable to handle. Carbon/Kevlar hybrids weave the two yarns together so one ply gives you carbon stiffness and aramid toughness, with the checkerboard that only a hybrid has. The 4.8 oz plain weave hybrid in yellow and black is the flat-panel choice; the 5.5 oz 2x2 twill hybrids, 50 in wide and about 0.009 in (0.23 mm) per ply, are the drape choice and come in blue, yellow, orange and red aramid. The black and orange twill runs 3K carbon in the warp and aramid in the fill, so it is stiff along the roll and tough across it; orient it accordingly.

Fabric	Weight	Weave	Width	Cured ply (approx.)	Where it goes
1.7 oz Kevlar 49, style 120	1.7 oz/yd² (58 g/m²)	Plain, 34 x 34	38 in	0.004 in (0.1 mm)	Abrasion and impact skin, inner ply on carbon panels, light paddle craft
5 oz Kevlar 49, style 281	5 oz/yd² (170 g/m²)	Plain, 17 x 17	38 in or 60 in	0.010 in (0.25 mm)	Canoe hulls, skid plates, structural aramid plies
4.8 oz carbon/Kevlar	4.8 oz/yd² (163 g/m²)	Plain	see the product page	about 0.008 in (0.2 mm)	Flat panels that need stiffness and impact toughness in one ply
5.5 oz carbon/Kevlar	5.5 oz/yd² (186 g/m²)	2x2 twill	50 in	0.009 in (0.23 mm)	Curved panels, visible hybrid parts, kart and bike bodywork

Why it only runs with epoxy

Glass fiber carries a silane coupling agent that gives polyester and vinyl ester something to grab. Aramid does not. Its surface is smooth and chemically inert, the bond to a polyester matrix is weak, and polyester shrinks as it cures and pulls away from the fiber; the laminate then fails at the fiber-resin interface long before the aramid is loaded, and a wet aramid laminate in polyester can be pulled apart by hand. Epoxy bonds to the fiber, cures with almost no shrink, and is tough enough to match it. Use a laminating epoxy measured exactly: 3:1 resin to hardener by volume for our medium hardener, or 5:1 by volume for West System 105/206. Cure schedule depends on the hardener and the shop temperature, so check the TDS. Plan on roughly 1:1 resin to fabric by weight for hand layup; aramid is bulky for its weight and will take more than a glass cloth of the same ounce weight, so wet out a test piece. Wet aramid does not go clear the way glass does. It goes from bright yellow to translucent amber; bright yellow after wet-out is dry fabric with no strength.

Working it

Cut it with serrated Kevlar shears, not fabric scissors, and tape both sides of the cut line first; it will dull a rotary cutter in a yard. Drill with a sharp brad point over a backer. Sand as little as you can with fresh paper, and put a fairing coat or a glass or carbon ply over any surface that will be seen or handled. Seal every edge with epoxy. Cutting and sanding aramid, and handling epoxy, call for a fitted P100 with organic vapor cartridges, nitrile gloves and eye protection.

Which one, by job

An abrasion and impact skin on a composite canoe or kayak hull, or the inside ply on a carbon panel that has to survive a strike: 1.7oz KEVLAR® Plain Weave Fabric Style 5120/120, 38 in wide, under a glass or carbon outer ply so it never sees sun. A flat panel that needs carbon stiffness with aramid toughness in a single ply: 4.8oz Plain Weave Carbon/Kevlar Fabric - Yellow/Black Hybrid Cloth. A curved or visible hybrid part, kart bodywork, a dash, a fairing, a board: the 5.5 oz twill in the colorway you want, 5.5oz Carbon/Kevlar Hybrid Fabric 2x2 Twill Weave (Black/Blue) - 1st Quality, 5.5oz Carbon/Kevlar Hybrid Fabric 2x2 Twill Weave (Black/Yellow) - 1st Quality, 5.5oz Carbon/Kevlar Hybrid Fabric - 2x2 Twill Weave (Black/Orange) or 5.5oz Carbon/Kevlar® Hybrid Fabric 2x2 Twill Weave (Black/Red) - 1st Quality, with the carbon warp along the stiff axis. A canoe hull from scratch is 5 oz style 281 plain weave with epoxy, and a worn stem is a skid plate in the same 5 oz tape. Size the epoxy with the resin calculator and add a margin for the aramid's bulk.

Frequently asked questions

Can you use polyester resin with Kevlar fabric?

No. Aramid has no coupling agent for polyester to bond to, and polyester shrinks on cure and pulls off the fiber, so the laminate delaminates at the fiber surface at a fraction of the fabric's strength. Use a laminating epoxy, 3:1 by volume for our medium hardener or 5:1 for West System 105/206, at roughly 1:1 resin to fabric by weight for hand layup. The same rule applies to the carbon/Kevlar hybrids.

Is Kevlar stronger than carbon fiber?

In tension per pound they are close and in impact aramid wins clearly, but in compression aramid gives up at about a fifth of its tensile strength while carbon does not, and carbon is far stiffer. A bending panel wants carbon or glass on the compression face and aramid where the hit lands. That is exactly what a 5.5 oz carbon/Kevlar twill does in one ply: carbon for stiffness, aramid for the strike.

Why does Kevlar turn yellow or brown?

Sunlight. Aramid degrades under UV, darkening from yellow toward brown and losing strength; very thin fabric in direct high-intensity sun can lose about half its tensile strength in days. Keep it under gelcoat, paint, a UV-stable clear coat, or an outer ply of glass or carbon, and store dry rolls out of the light. Bright yellow after wet-out is a different problem: that is dry fabric that never got resin.

How do you cut Kevlar fabric?

With serrated aramid shears, over a strip of masking tape on both sides of the line so the weave does not unravel. Ordinary scissors and rotary cutters go dull within a yard and start chewing the yarn instead of cutting it. Cut plies 1 in oversize and trim after cure with a fresh carbide blade or a cutoff wheel, then seal the edge with epoxy so the aramid does not wick water or fuzz.

What weight Kevlar for a canoe?

5 oz plain weave, style 281, is the standard canoe hull and skid plate cloth, about 0.010 in per ply in epoxy, with two to three plies in the hull and local extra at the stems. The 1.7 oz style 120 is the abrasion skin over a glass or carbon layup on a lighter boat rather than a hull fabric on its own. Both go under an outer glass ply or a painted surface, because aramid on the outside chalks and fuzzes in the sun.