Prepreg Out-of-Autoclave (OOA)

Prepreg Out-of-Autoclave cures fiber-reinforced prepregs under vacuum and controlled heat, delivering aerospace-grade laminates without high-pressure autoclaves for medium-complexity structures.

Overview

Prepreg Out-of-Autoclave (OOA) uses vacuum and controlled oven or press curing to consolidate advanced fiber/epoxy prepregs into high-performance composite laminates without an autoclave. You still get controlled fiber volume fraction, low void content, and good surface finish, but within the pressure limits of vacuum-only consolidation. This suits medium-complexity, medium-to-large parts where aerospace-level properties are needed, but full autoclave infrastructure is not justified.

OOA prepregs are engineered with specific resin rheology and vent paths to purge volatiles under vacuum, so tooling, bagging, and debulk discipline are critical. Expect good structural performance, but slightly lower fiber volume and tighter process windows than traditional autoclave prepreg. OOA is strong for monolithic laminates and sandwich panels, especially in aerospace, space, UAV, and high-end automotive work where moderate volumes, repeatability, and weight savings matter. Tradeoffs include more sensitivity to layup quality, tighter restrictions on laminate thickness and complexity, and less capability for extremely thick or highly contoured parts than full autoclave prepreg.

Common Materials

  • Carbon fiber/epoxy prepreg
  • Glass fiber/epoxy prepreg
  • Aramid fiber/epoxy prepreg
  • BMI prepreg
  • Cyanate ester prepreg

Tolerances

±0.010"

Applications

  • Fuselage and wing skin panels
  • Satellite and spacecraft structural panels
  • UAV wings and tail structures
  • Automotive body panels and roofs
  • Radomes and fairings
  • Composite access doors and control surfaces

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

Choose prepreg Out-of-Autoclave when you need near-aerospace laminate quality, moderate production volumes, and part sizes that make autoclave time or capital cost unattractive. It fits medium-thickness, moderately contoured structures with consistent layups and clear vacuum bag access. It’s ideal when you can design for vacuum-only consolidation and maintain tight process control on layup and curing.

vs Resin Transfer Molding

Pick OOA prepreg when you want tighter control of fiber orientation and stacking sequence, with certified prepreg systems and well-characterized allowables. It is better for thinner laminates and sandwich panels where dry preform handling or complex resin flow modeling for RTM would add risk or cost.

vs Vacuum-Assisted Resin Transfer (VARTM)

Choose OOA prepreg when you need cleaner, more repeatable fiber volume fraction and lower variability than typical VARTM, especially for qualified aerospace structures. It suits parts where controlled prepreg ply placement, tight thickness, and consistent mechanical properties matter more than very low material cost.

vs Prepreg Layup with Autoclave

Use OOA prepreg when autoclave access is limited, part size is too large, or the business case will not support autoclave capital or run cost. It’s a good fit if your performance requirements tolerate slightly lower fiber volume and higher porosity, and you can design laminates for vacuum-only consolidation.

vs Hand Lay-Up

Select OOA prepreg when you need much higher structural performance, lower voids, and better repeatability than wet hand lay-up can deliver. It suits programs that can justify freezer storage, controlled cure cycles, and more stringent process documentation for improved quality and traceability.

vs Compression Molding (Composites)

Go with OOA prepreg for larger, thinner, or more lightly loaded structures where surface area and laminate quality matter more than very high-volume, short-cycle production. It favors applications needing continuous fiber orientation control and large panel sizes that are impractical in matched-die compression tooling.

Design Considerations

  • Design for single-sided or simple matched tooling with robust vacuum bag access on all critical laminate areas
  • Limit laminate thickness and local build-ups where possible; very thick OOA sections are harder to fully consolidate under vacuum
  • Use generous radii and avoid tight inside corners to maintain fiber continuity and reduce bridging during layup and bagging
  • Standardize ply stacking sequences, orientations, and drop-off patterns to simplify layup and improve repeatability across builds
  • Define clear flat or reference datums on the tool side surface; expect more variation on the bag side and tolerance features accordingly
  • Call out allowable porosity, cosmetic requirements, and critical structural zones so the shop can tailor layup, debulks, and cure cycles effectively