As part of an innovative new HVAC development programme for modern rail vehicles, a European-based manufacturer required a reliable, flame-retardant sealing solution to be positioned between the HVAC unit and the carbody interface.
The HVAC module, mounted externally, demanded a material that would provide long-term environmental sealing while complying with the strictest fire, smoke and toxicity standards for rail interiors.
The chosen silicone sponge needed to ensure pressure-tight sealing, thermal insulation, and compliance with EN 45545-2 to Hazard Level 3 (HL3), the highest safety level required for passenger rail vehicles operating in tunnels or underground.
The Challenge
Design engineers faced several critical constraints in selecting a gasket material for the rail HVAC housing:
- High fire resistance requirements, specifically HL3 for interior exposure
- Thermal and weather stability due to the external positioning of the HVAC
- Low compression set to maintain an effective seal over time under mechanical stress
- Resistance to water ingress and particulate contamination
- Mechanical flexibility for ease of assembly and panel tolerance compensation
Additionally, the material would have to be produced in a custom thickness of 20mm to match the dimensional requirements of the HVAC flange and interface groove.
The HVAC Flange Seal for Modern Rolling Stock Solution
A high-performance closed-cell silicone sponge was identified as the ideal candidate, kSil® V-0 Soft, manufactured in compliance with EN 45545-2 (HL3), UL94 V-0, and other global transit standards.
This material’s closed-cell microstructure delivers an optimal balance of seal integrity, vibration dampening, and low water absorption, making it particularly well-suited for HVAC sealing in transit applications.
Following testing and sample prototyping, kSil® V-0 in 20mm thickness was selected for integration into the HVAC flange design. The material delivered strong sealing performance across thermal cycles, while enabling the design team to meet HL3 compliance without compromising mechanical integrity or requiring secondary sealing features.
The success of this project illustrates how specialist silicone formulations can enable system-level safety compliance and durability in high-risk transportation environments. For design engineers working on next-generation rail platforms, the use of closed-cell silicone sponge provides a reliable pathway to both safety certification and long-term mechanical performance.
Key Benefits
✅ HL3-compliant for rail interior applications
✅ Resilient closed-cell structure: prevents water ingress and enables long-term compression performance
✅ Operating temperature range: –60°C to +230°C
✅ Excellent weather and ozone resistance: ideal for exposed rail environments
✅ Available in wide thickness range (2–45mm): suited for custom flanges and engineered profiles
