EVA – Highly Versatile Material

EVA (Ethylene-Vinyl Acetate) foam is a widely used material in orthotic and prosthetic workshops due to its versatility, shock absorption, and ease of processing. Whether you’re a technician shaping custom orthotics or a prosthetist building a full lamination, understanding how to work effectively with EVA is key to achieving high-quality results that last.

This guide outlines the best practices for manufacturing with EVA foam across key processes including bonding, heating, cutting, sanding, and moulding. Following these tips can help extend product lifespan, improve fit and comfort, and reduce rework in clinical or production settings.

1. Selecting the Right EVA

EVA comes in a variety of densities, colours, and thicknesses, and different grades offer different levels of compression resistance, flexibility, and finish. For orthotic devices, choose a grade that suits the biomechanical requirements of the patient — softer for cushioning, firmer for support or posting.

• Low density (e.g. A20–A30): Excellent for top covers and cushioning layers.
• Medium density (e.g. A40–A50): Good all-rounder for mid-layers or full-length orthotics.
• High density (e.g. A60+): Ideal for base layers or devices requiring strong structural support.

2. Cutting and Shaping EVA

EVA can be easily cut using band saws, CNC routers, or sharp blades. For clean cuts:

• Use sharp, fine-toothed blades to avoid jagged edges or tearing.
• Secure the material to prevent movement or stretching while cutting.
• For layered products, pre-tack with light adhesive before cutting complex shapes to keep the sandwich stable.

3. Heating and Thermoforming

EVA is highly responsive to heat, making it ideal for custom moulding. Proper heating ensures the foam softens evenly without scorching or off-gassing.

• Use a heat gun, infrared oven, or convection oven set between 110–130°C depending on the grade.
• Heat until the material becomes flexible and slightly glossy but not melted or sagging.
• Press EVA over lasts, moulds, or casted forms and hold for 1–2 minutes until cool to retain shape.

Pro tip: Don’t overheat EVA. Doing so can cause bubbling, deformation, or degradation of foam structure — especially in lower-density grades.

4. Gluing and Bonding EVA

Effective bonding is critical when layering EVA or combining it with materials like leather, cork, or rigid plastics. Use adhesives specifically formulated for EVA foam:

• Polychloroprene adhesives (e.g. Renia Top-Fit or similar) provide strong, flexible bonds.
• Hot-melt glues work for quick setups but may lack long-term strength under load.

Steps for reliable bonding:

1. Ensure both surfaces are clean, dry, and lightly abraded if smooth.
2. Apply adhesive evenly to both surfaces and allow to tack off (usually 5–10 minutes).
3. Use a press or apply firm, even pressure to complete the bond.

Note: Avoid using cyanoacrylate or rigid-setting glues — these can crack or fail as the EVA flexes in use.

5. Sanding and Finishing EVA

Sanding is used to refine the shape, reduce bulk, or create smoother transitions in orthotic layers. For best results:

• Use belt sanders or sanding drums with medium grit (60–100).
• Always sand in a well-ventilated area or use dust extraction systems — EVA dust is fine and potentially irritating.
• Move evenly and avoid holding the EVA in one place too long to prevent heat buildup or gouging.

Sanding can also help ‘key’ the surface before gluing, especially for dense grades where bonding is more challenging.

6. Moulding and Laminating EVA

In advanced applications such as prosthetic sockets or foot orthotics, EVA can be laminated or vacuum-formed for precision shaping.

• Heat the EVA sheet until malleable (usually 2–3 minutes at 120°C).
• Place over a positive model and apply vacuum pressure using a vacuum former or bagging system.
• Allow full cooling (5–10 minutes) before trimming excess material.

For more complex lamination, EVA can be combined with thermoplastics or carbon-reinforced components to add structural strength while preserving comfort and shock absorption on the skin side.

7. Storage and Handling Tips

Proper storage of EVA foam ensures it stays clean, flat, and usable for long periods:

• Store in a cool, dry area away from direct sunlight.
• Avoid stacking heavy items on EVA sheets — this can create permanent creases.
• Label your offcuts by density or grade to reuse efficiently in workshop settings.

Conclusion

Working with EVA foam is a staple skill in orthotic and prosthetic manufacturing. By following best practices in cutting, bonding, heating, shaping, and finishing, you can consistently produce devices that meet clinical standards and enhance patient outcomes. For those using Aortha EVA materials, you’re already starting with a high-quality, medical-grade foam designed to perform across orthopaedic and technical applications.

Need help choosing the right EVA sheet or tooling for your workshop? Contact the Aortha team — we’re happy to help guide your material selection or processing setup.