solref\solimp Parameter Cheat Sheet

A practical reference for solref / solimp tuning

This cheat sheet provides recommended solref and solimp parameters for common materials in MuJoCo. These values serve as practical starting points, not absolute rules—MuJoCo’s contact model is approximate, and optimal settings depend on:

• mesh quality

• object mass & inertia

• simulation timestep (timestep)

• scene stability

Fine-tuning may still be required for precise results.

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🔧 Understanding Parameters

Solref

Controls contact stiffness and damping, defined as:

(solref_time_constant, solref_damping_ratio)

• Lower time constant → stiffer contact

• Damping ratio controls bounciness

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Solimp

Controls contact transition region, defined as:

(dmin, dmax, width, mid, power)

For most rigid objects, the default solimp is sufficient. You only need to change solimp when simulating very soft or special contact behaviors.

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📋 Recommended Material Parameters

Material Type	Typical Applications	Solref	Solimp	Physical Property Description
Rigid Metal / Concrete	Robot Bases, Connecting Rods, Ground Surfaces	0.002 1	0.9 0.95 0.001 0.5 2	Extremely hard. Almost no deformation upon impact and no rebound. Suitable for high-precision mechanical structures.
Hard Plastic / Hardwood	Building Blocks, Desktops, Housings	0.006 1	0.9 0.95 0.001 0.5 2	Hard yet stable. Slightly "softer" than metal, which can enhance simulation stability and reduce jitter.
Hard Rubber / Tires	Robot Foot Pads, Wheels	0.015 1	0.9 0.95 0.001 0.5 2	Slightly tough. Provides grip and allows minimal deformation upon contact.
Soft Silicone / Finger Tips	Soft Fingertips of Dexterous Hands, Sealing Rings	0.025 1	0.95 0.99 0.001 0.5 2	Soft. Allows visible compressive deformation at contact points, increasing contact area and facilitating grasping.
High-Elasticity Ball	Table Tennis Balls, Marbles	0.02 0.1	0.9 0.95 0.001 0.5 2	High resilience. Extremely low damping (0.1), retains most energy and rebounds after impact.
Sponge / Shock-Absorbing Foam	Cushion Pads, Anti-Collision Strips	0.04 4	0.8 0.99 0.001 0.5 2	Energy-absorbing. Over-damped (>1), similar to hitting dough—energy is quickly dissipated with no rebound.
Biological Soft Tissue	Human Skin, Muscles	0.03 1	0.9 0.95 0.001 0.5 2	Flexible and tough. Similar to soft silicone, but exhibits compliance over longer time scales.