Vacuum Bagging and Wet Layup Carbon Fiber for Makers: Building Composite Panels from Raw Cloth and Resin

This site's carbon fiber coverage so far is all about machining or cutting pre-made CF materials — CNC-machining G10/carbon fiber sheet, laser-cutting fiberglass, printing chopped-fiber-filled filament. None of that covers actually laying up your own carbon fiber parts from raw cloth and resin, which is a completely different (and for many enclosure, panel, and reinforcement projects, more useful) skill: wet layup and vacuum bagging. This guide covers the process end to end — laying cloth into a mold or onto a form, wetting it out with epoxy, and using a vacuum bag to compress the layup for a higher fiber-to-resin ratio and stronger, lighter final part than a hand-squeegeed layup alone.

Wet Layup vs. Vacuum Bagging: What's the Difference

MethodProcessResulting Part QualityEquipment Needed Wet layup (hand layup only)Cloth wetted with resin by brush/squeegee, left to cure under ambient pressureGood but resin-heavy, more voids, weaker strength-to-weightResin, cloth, brushes, mold or form Vacuum-bagged wet layupSame wet layup, then sealed in a bag and vacuum-compressed while curingSignificantly stronger, lighter, better surface finish on the tool-side faceAll of the above, plus vacuum pump, bagging film, breather/bleeder materials

The vacuum step does two things: it squeezes excess resin out of the laminate (a properly vacuum-bagged part should be noticeably lighter than the same layup cured without vacuum), and it compresses the layers together, eliminating the air voids that are the main source of weakness in a hand-laid composite part.

Materials You'll Need

• Carbon fiber cloth: plain weave or twill, typically 5.7oz (193 g/m²) for general panels, lighter (3-4oz) for skins over a foam or 3D-printed core.
• Epoxy resin system: a laminating epoxy (not casting epoxy — laminating resins are formulated for thin-film cure and better wet-out, casting epoxies are for thick pours and will overheat/crack in a thin laminate). Match hardener to your working time needs — slow hardener gives more working time for a first attempt.
• Mold or form: can be a 3D-printed or CNC-milled positive/negative mold (finished smooth and sealed with mold release wax or PVA release film), or a simple flat panel for a plain sheet layup.
• Peel ply: a nylon or polyester fabric layer placed directly on the wet laminate — it peels away after cure, leaving a clean, slightly textured surface ready to bond or paint without sanding.
• Breather/bleeder cloth: a thick, absorbent fabric layer that sits between the peel ply and the vacuum bag, giving excess resin somewhere to go and letting vacuum pressure distribute evenly across the whole part.
• Vacuum bagging film and sealant tape: nylon bagging film sealed around the perimeter with tacky sealant tape, connected to your vacuum line through a port fitting.
• Vacuum pump: a dedicated composites vacuum pump is ideal; a modified refrigeration/HVAC vacuum pump with a resin trap works for hobby-scale projects, but never use a pump not rated for continuous duty if you're curing over several hours.

Process: Step by Step

1. Prepare the mold: clean thoroughly, apply mold release wax (multiple coats, buffed out) or PVA release film. Any release failure here means you'll destroy the part removing it from the mold.
2. Cut your cloth to pattern, slightly oversized, with sharp scissors dedicated to composite work (resin residue ruins fabric shears fast).
3. Mix epoxy by weight, not volume, using a scale accurate to a gram — off-ratio epoxy is the single most common cause of a soft, under-cured, or brittle laminate.
4. Wet out the cloth on a clean surface first (or directly in the mold for simple shapes) using a brush or foam roller, working resin fully through the weave until it's translucent with no dry white patches.
5. Lay each ply into the mold, working out air bubbles with a laminating roller or squeegee from the center outward.
6. Apply peel ply directly over the wet laminate, then the breather/bleeder layer over that.
7. Bag it: lay the bagging film over the whole assembly, seal the perimeter with tacky tape, insert the vacuum port, and pull vacuum. Target 20-25 in-Hg — pulling too hard too fast can shift wet cloth out of position, so bring vacuum up gradually on a first attempt.
8. Check for leaks: a properly sealed bag holds vacuum with the pump disconnected; a hissing sound or a gauge that creeps back toward zero means a leak at the tape seal or around the vacuum port — find and reseal before the resin starts to gel.
9. Cure per the resin's schedule — most laminating epoxies want room temperature cure for several hours to overnight, with an optional post-cure warm-up (in an oven or heat gun-warmed enclosure) for maximum final strength once fully hardened.
10. Demold, peel off the peel ply, and trim the part to final dimensions on a bandsaw or with a cutoff wheel.

Where This Pairs With Existing Site Content

• Use a CNC-milled MDF or foam mold (following the CNC foam cutting guide) as a cheap, accurate positive form for a one-off panel.
• A 3D-printed mold, sealed and sanded smooth, works well for small parts — print the mold hollow with adequate wall thickness to resist the vacuum pressure without collapsing.
• Trim cured carbon panels on the CNC router the same way you'd machine pre-made carbon sheet, using the same dust-hazard precautions covered in that guide — cured epoxy/carbon dust is just as much a respiratory hazard as machining pre-made stock.

Safety Notes

Uncured epoxy resin and hardener are skin and respiratory sensitizers — repeated bare-skin contact can trigger a lasting allergic sensitization to epoxy generally, not just the specific product, so wear nitrile gloves for every mixing and layup step, not just "when it gets messy." Work in a ventilated area; epoxy off-gasses more than people expect during cure, especially in the first hour. Cutting or sanding cured carbon fiber releases fine conductive dust that's a respiratory hazard and can also short exposed electronics nearby — wear a proper respirator (not just a dust mask) and vacuum up dust rather than blowing it around, the same precautions covered in our carbon fiber CNC machining guide.

Wrapping Up

Vacuum-bagged wet layup is a genuinely different skill from anything else on this site involving carbon fiber — it's about building the material into a shape, not cutting or machining a shape out of pre-made stock. The learning curve is mostly about resin ratios, bag sealing, and working fast enough before gel time hits; once those are dialed in, it opens up strong, lightweight custom panels and enclosures that neither a 3D printer nor a CNC router can produce on their own.