---
type: process
name: "Filament Winding"
category: "Forming"
subcategory: "Composites"
materials: ["Composite"]
tolerances: "Inside diameter ±0.005–0.010 in (±0.13–0.25 mm), set by the mandrel. Wall thickness and outside diameter carry roughly ±0.5–1% because thickness builds in whole layers."
volumes: "100–500,000 parts per year"
lead_time: "6–16 weeks for mandrel and pattern development on a new part; hours per part in production once the winding program exists."
url: https://manufacturingprocesses.org/processes/forming/filament-winding
---

# Filament Winding

Filament winding wraps resin-impregnated continuous fiber onto a rotating mandrel in a controlled pattern, producing tubes and pressure vessels.

- **Category**: [Forming](https://manufacturingprocesses.org/processes/forming.md)
- **Family**: Composites
- **Materials**: Composite
- **Typical tolerances**: Inside diameter ±0.005–0.010 in (±0.13–0.25 mm), set by the mandrel. Wall thickness and outside diameter carry roughly ±0.5–1% because thickness builds in whole layers.
- **Surface finish**: The bore replicates the mandrel and is smooth. The outer surface shows the winding pattern as a visible fiber texture; a peel ply, shrink tape, or surfacing veil is used where a smoother or paintable exterior is needed.
- **Typical volumes**: 100–500,000 parts per year
- **Lead time**: 6–16 weeks for mandrel and pattern development on a new part; hours per part in production once the winding program exists.

## Overview

Filament winding lays resin-impregnated continuous fiber onto a rotating mandrel along a computer-controlled path, so every fiber follows the load line the designer chose. It produces the highest fiber volume fractions of any laminating process — typically 60–70% wet wound — because winding tension consolidates each layer as it is laid.

The signature result is netting analysis's optimum helical angle of 54.7° for a closed-end cylindrical pressure vessel, the angle at which fiber stresses balance the 2:1 ratio of hoop to axial stress in a thin-walled cylinder. Real vessels combine hoop windings near 85–90° with helical and polar passes to reach that balance across domes and cylinder alike.

Because fiber must be laid in tension over a convex surface, filament winding makes only surfaces of revolution and gentle variations on them: CNG and hydrogen cylinders, pipe and pressure vessels, rocket motor cases, drive shafts, rollers, and poles. It is highly automated, so labor per part is low and volumes reach hundreds of thousands.

## How it works

1. **Prepare the mandrel.** The mandrel defines the inside surface. It may be a reusable steel or aluminum shaft withdrawn afterward, a collapsible or segmented mandrel for closed shapes, a soluble sand or plaster core washed out after cure, or a permanent liner that stays in the part — an aluminum liner for a Type III cylinder or a blow-molded HDPE or polyamide liner for Type IV.
2. **Impregnate.** In wet winding, tow passes through a resin bath and a set of wiper dies or rollers that meter resin content. Towpreg and prepreg tape winding skip the bath and give tighter control of resin fraction at higher material cost.
3. **Wind.** The mandrel rotates while a delivery eye traverses. The ratio of traverse speed to rotation sets the winding angle: roughly 85–90° for hoop windings that carry hoop stress, 15–80° for helical passes that carry combined loads, and 5–15° for polar windings that run over the domes of a closed vessel. Fiber tension — commonly a few newtons up to tens of newtons per tow — consolidates the laminate and squeezes out excess resin.
4. **Build the pattern.** Layers are wound in a repeating pattern that closes on itself after a whole number of circuits, so coverage is uniform. Modern machines plan these patterns automatically along with the dome turn-around geometry.
5. **Cure.** Polyester and vinyl ester systems cure at ambient to about 180 °F (80 °C); epoxies at 250–350 °F (120–180 °C). Curing is done with the mandrel still rotating so resin cannot drain to the bottom of the part before gelation.
6. **Extract and finish.** The mandrel is withdrawn, collapsed, or dissolved. Ends are trimmed, bosses and fittings installed, and pressure vessels are proof tested and often autofrettaged — pressurized beyond the liner's yield point so the metal liner is left in beneficial compression.

## Design guidelines

### Convex surfaces of revolution only
Fiber under tension takes the shortest geodesic path over the mandrel. It will not stay in a concave region and will slip off a surface that turns away from it. Any concavity, sharp shoulder, or re-entrant feature must be added afterward as a bonded or laid-up detail.

### Winding angle follows the load
Hoop stress in a thin-walled cylinder is twice the axial stress, so a vessel wound entirely at one angle is inefficient. Use hoop windings near 90° for the cylindrical section and helical windings at 54.7° or lower where axial and dome loads must be carried. For a drive shaft loaded in torsion, ±45° is the efficient answer; for a bending-loaded pole, low-angle windings near 0° carry the load.

### Dome geometry
The dome profile of a pressure vessel is set by the fiber path, not chosen freely. Geodesic and near-geodesic dome contours exist precisely so fiber does not slip; specifying an arbitrary dome shape forces non-geodesic winding with friction-dependent stability.

### Boss and port design
Openings must be reinforced and the fiber turned around a boss of adequate diameter. A polar boss too small in relation to the vessel diameter causes fiber build-up and a resin-rich, weak turnaround region.

### Wall thickness and tolerance
Inside diameter is set by the mandrel and is the accurate dimension — typically ±0.005–0.010 in (±0.13–0.25 mm). Wall thickness builds up in whole layers and varies with pattern and tension, so outside diameter carries roughly ±0.5–1% of the wall.

### Liner compatibility
For Type IV vessels, the thermoplastic liner must survive the resin cure temperature. This constrains resin selection to systems that cure below the liner's softening point, or requires a liner material chosen for the cure cycle.

### Design to code
Composite pressure vessels are governed by design codes that require burst pressures of roughly 2.25–3.5 times service pressure depending on cylinder type and jurisdiction, plus cycle and environmental qualification. Establish the applicable code before choosing a layup.

| Feature | Recommended | Limit | Why |
| --- | --- | --- | --- |
| Surface geometry | Convex, surface of revolution | No concavity | Fiber under tension will not follow it |
| Helical angle, closed vessel | 54.7° | Set by netting analysis | Balances 2:1 hoop-to-axial stress |
| Hoop winding angle | 88–90° | 85° | Efficient hoop stress carriage |
| Fiber volume fraction | 60–65% | 70% | Above this, resin starvation |
| ID tolerance | ±0.010 in (0.25 mm) | Mandrel-limited | Mandrel defines the bore |
| Wall build-up | Whole layer increments | — | Thickness is quantized by pattern |

## Cost drivers

Filament winding is a machine-hour process with very little touch labor, which is what separates it economically from hand layup. Cost per part is driven by winding time — a function of part surface area, layer count, and how fast the machine can traverse without disturbing fiber placement — plus material.

Mandrels are the tooling cost, and the type chosen changes the economics completely. A reusable steel mandrel amortizes across thousands of parts. A soluble sand or plaster mandrel is consumed every cycle and adds both material and washout labor. A permanent liner is part of the product, so it appears as material rather than tooling.

Material is a large share of a wound part because fiber volume fraction is high by design. Wet winding with bulk roving and resin is the cheapest feedstock route; towpreg costs more but reduces variability and eliminates the resin bath.

Volume breakpoints: filament winding becomes attractive at roughly 100 parts a year where a reusable mandrel can be used, and scales to hundreds of thousands for cylinders and pipe. Below that, hand [composite laminating](/processes/forming/composite-laminating) over a male plug is usually cheaper.

1. Design for a reusable mandrel — extraction geometry is worth more than shape freedom.
2. Keep the shape a true surface of revolution; every non-axisymmetric feature is added labor.
3. Use hoop windings where hoop stress dominates instead of thickening the whole laminate.
4. Specify glass where stiffness allows and reserve carbon for the layers that need it — hybrid layups are routine.
5. Batch parts on one mandrel where geometry permits, then cut them apart after cure.

## FAQ

### Why is 54.7 degrees the optimum winding angle?

In a thin-walled closed cylinder under internal pressure, hoop stress is twice the axial stress. Netting analysis — which assumes the fibers carry all the load and the resin none — gives an angle whose tangent is the square root of two, or about 54.7°, at which fiber tension balances that 2:1 ratio exactly. Real vessels combine this with hoop and polar windings.

### What shapes can filament winding produce?

Convex surfaces of revolution: cylinders, cones, spheres, and closed pressure vessels with domed ends. Fiber laid under tension follows a geodesic path and will not stay in a concave region, so concavities, flanges, and re-entrant features must be added afterward as bonded or hand-laid details.

### What fiber volume fraction does filament winding achieve?

Typically 60–70% wet wound, higher than hand layup or vacuum-bagged laminating, because winding tension consolidates each layer as it is placed and squeezes out excess resin. Since laminate stiffness scales nearly linearly with fiber volume fraction, this is the process's main structural advantage.

### What is the difference between Type III and Type IV pressure vessels?

Both are fully wrapped composite cylinders. A Type III uses a metallic liner, usually aluminum, which carries some load and provides the gas barrier. A Type IV uses a thermoplastic liner that provides only the barrier, making the vessel lighter but requiring a resin system that cures below the liner's softening temperature.

### How is the mandrel removed from a closed vessel?

Four ways: withdraw a tapered or straight mandrel through an open end, collapse a segmented mandrel and remove it in pieces, wash out a soluble sand or plaster core, or leave a permanent liner in place as part of the finished product — which is how pressure vessels are made.

### What tolerance can filament winding hold?

The bore is accurate because the mandrel defines it, typically ±0.005–0.010 in (±0.13–0.25 mm). Wall thickness builds up in whole layers and varies with pattern and tension, so the outside diameter carries about ±0.5–1% of the wall thickness.

## Alternative processes

- [Composite Laminating](https://manufacturingprocesses.org/processes/forming/composite-laminating.md): Composite laminating lays reinforcing fiber into a mold and consolidates it with resin, curing into a stiff, light monocoque part.
- [Pultrusion](https://manufacturingprocesses.org/processes/forming/pultrusion.md): Pultrusion pulls continuous fiber through a resin bath and a heated die, curing it into a constant-section composite profile of unlimited length.
- [Metal Spinning](https://manufacturingprocesses.org/processes/forming/metal-spinning.md): Metal spinning presses a rotating metal disc against a mandrel with a roller or hand tool, forming it into an axially symmetric hollow shape.
- [Deep Drawing](https://manufacturingprocesses.org/processes/forming/deep-drawing.md): Deep drawing pushes a sheet metal blank through a die with a punch so the metal flows into a seamless cup or box deeper than its own diameter.
- [Rotation Molding](https://manufacturingprocesses.org/processes/forming/rotation-molding.md): Rotational molding tumbles powdered polymer inside a heated mold on two axes so it fuses into a seamless, stress-free hollow part with a uniform wall.

## Related processes

- [Composite Laminating](https://manufacturingprocesses.org/processes/forming/composite-laminating.md): Composite laminating lays reinforcing fiber into a mold and consolidates it with resin, curing into a stiff, light monocoque part.
- [Pultrusion](https://manufacturingprocesses.org/processes/forming/pultrusion.md): Pultrusion pulls continuous fiber through a resin bath and a heated die, curing it into a constant-section composite profile of unlimited length.
- [DMC and SMC Molding](https://manufacturingprocesses.org/processes/forming/dmc-and-smc-molding.md): DMC and SMC molding compression-molds a pre-mixed dough or sheet of chopped fiber and thermoset resin into a stiff, dimensionally stable part.
- [Rotation Molding](https://manufacturingprocesses.org/processes/forming/rotation-molding.md): Rotational molding tumbles powdered polymer inside a heated mold on two axes so it fuses into a seamless, stress-free hollow part with a uniform wall.
- [Blow Molding](https://manufacturingprocesses.org/processes/forming/blow-molding.md): Blow molding inflates a heated plastic tube or preform against the walls of a mold with compressed air, producing hollow one-piece containers and tanks.

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*Source: [Manufacturing Processes](https://manufacturingprocesses.org/processes/forming/filament-winding)*

*Last updated: August 11, 2026*