Introduction: The Safety Standard That Changed Everything

On July 1, 2026, China's GB 38031-2025 mandatory national standard for electric vehicle traction batteries officially took effect. The updated regulation represents a fundamental shift in battery safety philosophy—from providing occupants with a five-minute escape window to requiring that battery systems must not catch fire or explode even after thermal runaway occurs.

This is not a marginal tightening of requirements. The new standard mandates that any smoke released during a thermal runaway event must not pose a hazard to vehicle occupants, and battery manufacturers must now pass a dedicated thermal propagation test verifying that a single-cell failure does not cascade into a full system fire or explosion.

Against this backdrop, material selection for battery pack insulation, sealing, and cushioning has become a critical engineering decision. The UL94 V-0 silicone foam tube has emerged as a key enabling material—not because it is the only option, but because it simultaneously addresses the multiple safety and performance requirements that modern EV battery packs demand.

What Is UL94 V-0 and Why Does It Matter for EV Batteries?

The UL94 Standard Explained

UL94 is the standard test method established by Underwriters Laboratories for assessing the flammability of plastic materials. The rating system progresses from HB (horizontal burn) through V-2, V-1, and V-0—with V-0 representing the highest level of flame resistance for vertical burn testing.

A material achieving UL94 V-0 must meet the following criteria:

• Self-extinguishes within 10 seconds after removal of the ignition source
• No molten dripping that could ignite cotton beneath the specimen
• No release of toxic dense smoke

Why This Rating Is Non-Negotiable in EV Battery Packs

In a lithium-ion battery pack, thermal runaway can generate gas jets exceeding 800°C with ejection velocities surpassing 200 m/s. If surrounding materials are not flame-retardant, these jets can ignite adjacent components and trigger cascading failure across the entire module.

A UL94 V-0 rated silicone foam tube provides a critical fire barrier function: in the event of a cell failure, it self-extinguishes rather than propagating flame, buying valuable time for the battery management system to respond and for occupants to evacuate.

The Five Critical Protection Functions of Silicone Foam Tube in EV Battery Packs

A modern EV battery pack is a complex assembly where materials must perform multiple functions simultaneously. The UL94 V-0 silicone foam tube addresses five distinct requirements:

1. Flame Retardancy — The Fire Barrier

The primary function of a flame retardant silicone foam tube in battery safety is to act as a thermal and fire barrier between battery cells, modules, and high-voltage conductors.

Silicone foam achieves UL94 V-0 through a halogen-free low-smoke flame retardant formulation. Upon exposure to flash arc heating or short-circuit thermal surges, inorganic fillers in the silicone compound initiate endothermic dehydroxylation to dilute localized oxygen. The solid oxides then fuse with the remaining silica backbone to form a non-combustible ceramic char layer that halts internal damage.

Recent research published in Nano-Micro Letters demonstrated the effectiveness of this mechanism: a 3mm layer of ceramifiable silicone foam composite prevented thermal runaway propagation beyond the initiating cell in tests using commercial 37Ah prismatic lithium-ion cells. By contrast, unprotected modules experienced full thermal runaway propagation within seconds, while modules using conventional silicone foam merely delayed the process.

2. Compression Cushioning — Managing Cell Breathing

Battery cells undergo continuous expansion and contraction during charge and discharge cycles—a phenomenon known as 'cell breathing.' Without appropriate cushioning, this mechanical stress can damage cell casings, degrade electrical connections, and reduce battery lifespan.

Silicone foam tube serves as a compression cushion that accommodates this movement while maintaining consistent pressure across the cell surface. The critical metric here is compression set—the material's ability to recover its original thickness after prolonged compression.

Yutian's UL94 V-0 silicone foam tube achieves compression set ≤15% (and ≤10% for platinum-cured grades), ensuring reliable cushioning performance over the battery's entire service life. This is particularly important in cell-to-body (CTB) battery designs, where the battery pack forms part of the vehicle structure and must withstand additional mechanical loads.

3. Thermal Insulation — Slowing Heat Propagation

While the flame barrier function addresses active fire, thermal insulation addresses the pre-ignition phase: slowing the rate at which heat from a failing cell transfers to adjacent cells.

The closed-cell structure of silicone foam tube traps static air within thousands of independent micro-cells. Because stagnant air has a thermal conductivity of approximately 0.026 W/m·K, the overall material achieves thermal conductivity below 0.06 W/m·K.

Recent advances in ceramifiable silicone foam have pushed this even lower—to 0.046 W/m·K, approximately 50% lower than pristine silicone foam—while maintaining stable elasticity from -40°C to 300°C.

4. Electrical Insulation — Preventing Short Circuits

High-voltage battery systems operate at 400V to 800V, making electrical insulation a critical safety requirement. Any conductive path between high-voltage components can result in arc faults, short circuits, and potential fire.

Silicone foam tube provides high dielectric strength insulation, blocking moisture, dust, and contaminants that could create conductive paths. The closed-cell structure is particularly important here—it prevents water absorption that would compromise insulation resistance.

5. Mechanical Protection — Vibration and Impact Damping

EV battery packs are subjected to continuous vibration during vehicle operation and must withstand impact loads during collisions. The new GB 38031-2025 standard includes an underbody impact test specifically designed to assess battery protection in collision scenarios.

Silicone foam tube provides excellent shock absorption, protecting delicate battery cells from vibrations and external impacts. The cellular structure deforms under load, absorbing energy that would otherwise transfer to the cells.

Technical Specifications: What to Look For

Applications in EV Battery Packs

High-Voltage Harness Protection

The orange high-voltage cables in an EV battery pack represent a critical fire risk during a thermal event. UL94 V-0 silicone foam tube is used as over-sleeving for these conductor bundles, providing both flame-retardant barriers and abrasion damping to protect against vehicle road vibration fatigue.

Cell-to-Cell Cushioning

Between adjacent battery cells, silicone foam tube provides compression cushioning that accommodates cell breathing while maintaining consistent pressure. This is essential for maintaining electrical contact reliability and preventing cell casing deformation.

Module-to-Module Thermal Barriers

Between battery modules, silicone foam tube acts as a thermal and fire barrier. In the event of a single-module failure, it prevents heat and flame from propagating to adjacent modules—directly supporting the GB 38031-2025 requirement that thermal runaway must not cascade beyond the initiating cell.

Battery Pack Sealing

The battery pack enclosure must maintain IP67 or higher sealing to prevent moisture ingress. Silicone foam tube serves as a compression seal around pack edges, connector interfaces, and cooling line penetrations—blocking water, dust, and contaminants that could cause electrical faults.

Cooling Line Insulation

For battery packs using liquid cooling systems, silicone foam tube provides thermal insulation around coolant lines, preventing condensation formation and reducing parasitic heat loss that would reduce cooling efficiency.

Comparison: Silicone Foam vs. Alternative Materials

Silicone foam tube is the only material that simultaneously delivers UL94 V-0 flame retardancy, wide temperature range, compression cushioning, electrical insulation, and thermal insulation—making it uniquely suited to the multi-functional requirements of EV battery packs.

How to Select a Reliable UL94 V-0 Silicone Foam Tube

1. Verify the Flame Rating Certification

Request UL94 V-0 test reports from a recognized third-party laboratory. The rating must apply to the finished product at the specified thickness—not just the raw material.

2. Confirm the Curing Method

Platinum-cured silicone foam is the standard for high-purity applications, offering:

• No peroxide residues
• No odor
• Compression set ≤10%
• Consistent electrical insulation properties

3. Request Thermal and Mechanical Data

Ask for:

• Thermal conductivity (λ value)
• Compression set (after 22 hours at 70°C)
• Operating temperature range (continuous and short-term)
• Dielectric strength (breakdown voltage)

4. Evaluate Dimensional Consistency

Uniform wall thickness and cell structure across the entire length indicate good manufacturing control. Check for smooth surfaces without powder shedding or delamination after bending.

5. Consider Customization Requirements

A capable manufacturer should support:

• Custom inner diameter and wall thickness
• Custom density and hardness
• Optional ceramifiable formulation for enhanced thermal protection
• Fast sampling for design validation

Key Takeaways

1. GB 38031-2025 represents a fundamental shift in EV battery safety—from a five-minute warning to an absolute requirement that battery systems must not catch fire or explode after thermal runaway.
2. UL94 V-0 silicone foam tube provides five critical protection functions: flame retardancy, compression cushioning, thermal insulation, electrical insulation, and mechanical damping.
3. The ceramifiable mechanism of advanced silicone foam forms a non-combustible ceramic barrier that has been shown to confine thermal runaway to a single cell in full-module testing.
4. Compression set ≤15% (≤10% for platinum-cured grades) ensures reliable cushioning performance throughout the battery pack's service life.
5. Thermal conductivity ≤0.06 W/(m·K) slows heat propagation during thermal events and insulates the battery from external temperature extremes during normal operation.

Frequently Asked Questions