Auxetic Shoe Insoles for Shock Absorption

ISEF Category: Engineering Technology: Statics and Dynamics

Subcategory: Mechanical Engineering  ·  Difficulty: Advanced  ·  Setup: School Lab  ·  Time: Full Year

The Hook

A thin insole can change how hard your body gets hit with every step. That matters more than you might think, because sports shoes, work boots, and prosthetic liners all depend on the same idea. Your project asks a simple question with real engineering stakes, can shape beat thickness?

What Is It?

An auxetic material gets wider when you pull it and narrower when you squeeze it. Most materials do the opposite. That strange motion can help an insole spread impact forces over a larger area, which may lower the peak force your foot feels.

Think of a snowshoe versus a stiletto heel. Both support weight, but one spreads load over a big area. Auxetic insoles try to do something similar inside a thin layer. Instead of just being soft, they use geometry, often a repeating cut pattern or lattice, to change shape in a smart way under impact.

For your project, you can compare an auxetic insole to a normal foam insole of the same thickness. You can measure impact force with a load cell, then use high-speed phone video to see how the structure compresses. An IMU, which is a small motion sensor, can help you study how the insole changes gait during walking or running.

Why This Is a Good Topic

This is a strong science fair topic because you can test real design choices, not just build something and hope it works. You can change the pattern geometry, the material, or the thickness, then measure impact response with clear numbers. The topic connects to footwear, injury prevention, sports gear, and protective equipment. You can also learn structural mechanics, signal analysis, and experimental design, all skills that matter for engineering research.

Research Questions

• How does auxetic lattice geometry change peak impact force compared with a solid foam insole of the same thickness?
• What is the effect of insole thickness on energy absorption per unit mass for auxetic and non-auxetic designs?
• Does a auxetic insole reduce force transmission better than a standard insole under repeated drop impacts?
• To what extent does cell angle or cut pattern change compression recovery after impact?
• Which material choice gives the best balance of shock absorption and stiffness for a thin insole?
• How does an auxetic insole change gait symmetry, step variability, or vertical acceleration during walking?

Basic Materials

• Shoebox or similar test frame for alignment and repeatability.
• Sample insole materials such as EVA foam sheets, craft foam, or silicone foam.
• Hobby knife or laser-cut access for making repeatable lattice patterns.
• Digital kitchen scale with 0.1 g accuracy.
• Ruler or calipers for measuring thickness and pattern size.
• Smartphone with slow-motion video.
• Basic tripod or phone clamp.
• Load cell with amplifier or force sensor.
• Hanging weight set or drop mass.
• Hard impact surface such as plywood or steel plate.
• Tape, marker, and grid paper for alignment.
• Simple straps or test shoe shell for gait trials.
• Wearable IMU or phone-based motion sensor app for gait data.

Advanced Materials

• Universal testing machine for compression testing.
• High-speed camera with calibrated frame rate.
• Instrumented impact rig with load cell and guided drop mechanism.
• Digital force amplifier and data acquisition system.
• 3D printer for lattice prototypes.
• CAD software for pattern design.
• Thin pressure mapping film or pressure sensor array.
• Motion-capture IMU system for gait analysis.
• Materials samples with different durometers and densities.
• Vernier calipers or micrometer for dimensional checks.
• Adhesives or bonding tools for layered prototypes.
• Statistical analysis software for repeated-measures testing.

Software & Tools

• Tracker: Tracks frame-by-frame deformation from high-speed video and extracts displacement data.
• ImageJ: Measures compression area, shape change, and recovery from still frames.
• Python: Processes force signals, calculates peak force, and compares design groups.
• RStudio: Runs statistics and plots repeated-trial comparisons.
• Excel: Organizes raw impact and gait data for quick inspection and charting.

Experiment Steps

1. Define the one performance metric you care about most, such as peak force, energy absorbed, or force per millimeter of thickness.
2. Choose a baseline insole and one auxetic geometry so you can make a fair side-by-side comparison.
3. Plan a test rig that keeps drop height, alignment, and contact surface the same across trials.
4. Build a calibration plan that converts load cell output and video motion into matching force and deformation data.
5. Decide how many repeated trials you need for each design so your comparison has enough statistical power.
6. Add a gait study only after your impact testing works, then check whether the insole changes real walking motion.

Common Pitfalls

• Using a pattern that looks auxetic on paper but does not actually expand laterally under compression.
• Comparing prototypes with different thicknesses or densities, which makes the result about material differences instead of geometry.
• Letting the drop mass land off-center, which creates bending and hides the true compression response.
• Recording video without fixed lighting or camera position, which makes deformation tracking noisy and inconsistent.
• Treating one lucky trial as proof, which ignores sample-to-sample variation and repeated impact wear.

What Makes This Competitive

A stronger project will separate geometry effects from material effects with clean controls. You can go beyond a simple before-and-after test by comparing several lattice patterns, then using statistics to show which design really changes impact response. A more advanced entry could connect impact data to gait data, so you can ask whether better shock absorption also changes motion in a meaningful way. Judges like projects that explain why a design works, not just whether it worked once.

Project Variations

• Test the same auxetic idea in a heel insert instead of a full insole to see whether impact location changes the result.
• Compare 3D-printed lattice inserts with laser-cut foam inserts to separate material behavior from pattern geometry.
• Add a second analysis layer by measuring recovery time or permanent set after repeated impacts instead of only peak force.

Learn More

• MIT OpenCourseWare, Mechanics of Materials: Search MIT OpenCourseWare for lectures on stress, strain, and energy absorption.
• NIST Materials Data: Use NIST resources to look up mechanical properties and testing concepts for polymers and foams.
• NASA Tech Briefs: Search for articles on lattice structures, impact mitigation, and lightweight structural design.
• PubMed: Search for review articles on auxetic materials, footwear biomechanics, and plantar loading.
• Journal of Applied Mechanics: Read peer-reviewed papers on deformation, impact, and structural response through your library or journal search.