Passive Cooling for Passenger Bus Cabins
The Challenge
How can bus operators protect passenger comfort under peak solar load, across A/C and non-A/C fleets?
Solar heat gain is a persistent comfort and cost problem for bus operators. Standard white PU composite roofs can exceed 122°F (50°C) in direct sunlight, driving up cabin temperatures, straining A/C systems where installed, and leaving passengers to bear the heat.
The Solution - PolyFrost
A passenger bus manufacturer applied PolyFrost, ChillSkyn’s passive cooling coating, to the standard white-painted composite roof of a passenger bus. Performance was monitored against an identical uncoated control bus under real-world conditions.
What is PolyFrost®?
PolyFrost is a patented spray-applied passive cooling coating, engineered to reduce heat load on sun-exposed assets, such as refrigerated transport, containers, and industrial equipment.
Reduces solar heat load
Prevents surface heat from becoming an internal temperature problem.
Lowers cooling workload
Cooling systems run fewer hours. Less runtime, less energy, less mechanical strain.
Scalable and easy to apply
Standard spray equipment, just like paint, in under 12 hours. Retrofit or factory spec.
Protects asset economics
Supports resale position, maintenance planning, and replacement timing.
Results
Field Trial
- Huehuetoca, MX - June 2026
20-day monitoring period, sunny and rainy conditions - Exterior roof surface under direct sunlight.
- 1 control • 1 test
Identical buses, standard white-painted composite roofs
Method
- Temp sensors mid-cabin (interior air + ceiling surface)
- Doors and windows closed
- Exterior roof temp measured with infrared thermal imaging
White PU Paint 105.8°F (41°C) PolyFrost 73.4°F (23°C)
Roof is 32.4°F (18°C) lower than white PU paint roof.
Performance Comparison | |
|---|---|
Peak cabin air temperature reduction up | ↓ up to 10°F (6°C) |
Exterior roof surface temp difference PolyFrost vs. white PU paint | ↓ 18-27°F (10-15°C) |
Cooling benefit maintained in rain | ✓ |
Key Impacts
Increased Passenger Comfort
Up to 10°F (6°C) cooler inside at peak sun, a difference passengers feel immediately.
All-Weather Performance
A measurable cooling advantage held even through rainfall.
A Path to Fleet Scale
Applies to new builds or in-service buses alike with standard spray equipment.
Climate note: This trial spanned the rainy season. Operators in drier, high-solar climates should expect results at the upper end of observed performance.