Prepreg Out-of-Autoclave (OOA)

Prepreg out-of-autoclave (OOA) makes high-fiber composite laminates using vacuum-bagged prepreg cured in an oven, balancing performance with lower capital than autoclaves.

Overview

Prepreg Out-of-Autoclave (OOA) is a prepreg layup process where reinforcement pre-impregnated with partially cured resin is vacuum-bagged on a tool and cured in an oven instead of an autoclave. OOA prepregs are formulated to vent air/volatiles under full vacuum so you can achieve aerospace-grade laminates without autoclave pressure.

Choose OOA when you need high fiber volume, controlled resin content, and good surface finish on one tool side, but your part size, budget, or supply chain can’t support autoclave curing. It’s common for medium volumes, large parts, and prototype-to-production programs.

Tradeoffs: void control and interlaminar properties are more sensitive to layup discipline, bagging details, and cure cycle than autoclave prepreg; thick laminates and complex internal geometry raise risk. Expect post-cure trimming/secondary machining and careful process controls (debulks, vent paths, leak rate targets) to hit quality consistently.

Common Materials

  • Carbon fiber/epoxy OOA prepreg
  • Glass fiber/epoxy OOA prepreg
  • Carbon fiber/bismaleimide (BMI) prepreg
  • Aramid/epoxy prepreg
  • Epoxy film adhesive
  • Nomex honeycomb core

Tolerances

±0.010–0.030 in (trimmed); thickness typically ±0.005–0.020 in depending on ply count

Applications

  • UAV wing skins and control surfaces
  • Aircraft interior panels and fairings
  • Satellite instrument panels and brackets
  • Motorsport body panels and aero surfaces
  • Radomes and RF-transparent covers
  • Composite sandwich panels with honeycomb core

When to Choose Prepreg Out-of-Autoclave (OOA)

OOA prepreg is a good fit for parts that need controlled laminate quality, low void content, and repeatable fiber/resin ratio without autoclave infrastructure. It works well for medium volumes and larger tools where oven capacity is easier to scale than autoclave pressure vessels. Expect best results on parts that can be vacuum-bagged reliably with clear vent paths and accessible trim features.

vs Resin Transfer Molding

Choose OOA prepreg when fiber orientation control, ply-by-ply tailoring, and tight resin content are priority and you can accept manual layup labor. OOA avoids injection flow risks (dry spots, race tracking) on complex laminates and supports sandwich constructions and local doublers cleanly.

vs Vacuum-Assisted Resin Transfer (VARTM)

Choose OOA when you need higher fiber volume fraction and more consistent mechanical properties than typical infusion, especially for thin skins and performance-critical laminates. OOA also reduces variability from resin flow media, inlet strategy, and infusion timing, at the cost of higher material cost and freezer-life management.

vs Prepreg Layup with Autoclave

Choose OOA when autoclave size/cycle cost is the constraint or the part is too large to fit available autoclaves. Autoclave prepreg still wins for maximum compaction, lowest porosity margin, and robust thick-laminate quality; OOA is the practical middle ground when oven cure and strong process discipline can meet requirements.

vs Compression Molding (Composites)

Choose OOA when you need continuous-fiber laminates with tailored stacking sequences rather than chopped/SMC-style architectures. OOA suits lower-to-mid volumes and larger, flatter skins where matched-metal tooling and high press tonnage would be cost-prohibitive.

vs Hand Lay-Up

Choose OOA when you need tighter control of resin content, better repeatability, and cleaner shop-floor handling than wet layup. OOA prepreg reduces mix/ratio errors and improves cosmetic quality, but requires cold storage, controlled layup conditions, and disciplined vacuum bagging.

Design Considerations

  • Provide trim allowance and define trim datum surfaces; net-edge layup increases scrap risk and quoting uncertainty
  • Minimize abrupt thickness changes; taper ply drop-offs (scarf/stepped drops) to reduce resin-rich zones and delamination risk
  • Design for reliable vacuum bagging: include flange widths, sealant tape land, and vent paths for air/volatile removal
  • Specify core details clearly (core type, thickness, perforation/venting, edge closeout method) to avoid rework and porosity traps
  • Call out critical surfaces and which side is tool-side; expect better finish and dimensional control on the tool surface
  • Include inspection/acceptance requirements up front (void limits, NDI method, witness panels) so the shop can build the right process plan