On the evening of March 19, Lei Jun shared a video on his personal social account: "Today, I climbed to the rooftop to test something fun for everyone." He dropped a watermelon from the rooftop of the Xiaomi car factory, which is equivalent to the height of a six-story building, and surprisingly, the watermelon remained intact.

Lei Jun said, the surface of this watermelon is coated with a "bulletproof coating" from car batteries, which not only has excellent puncture and tear resistance but is also extremely wear-resistant, with a protection level comparable to that of tank armor. It is reported that this experiment was conducted on internal factory roads, and the road had been cleared in advance to ensure safety.

This bulletproof coating has the following characteristics:

High strength and wear resistanceThe tensile strength and impact resistance of the coating are four times those of traditional PVC materials, the wear resistance can reach ten times that of carbon steel, and the surface scratch resistance is ten times that of traditional PVC materials.

excellent flame retardant performanceIts flame retardant rating reaches UL94 V0, with a self-extinguishing time of less than 10 seconds.

good chemical stability and environmental friendliness:The coating exhibits good chemical stability and environmental friendliness.

Xiaomi's latest released SU7 Ultra model adopts this "bulletproof coating" technology, especially at the bottom of the battery pack, which can effectively prevent cell damage caused by bottoming out or foreign object impacts during vehicle operation, thereby enhancing safety performance.

"The core material of 'bulletproof coating' is polyurea material. So, what is polyurea material?"

Polyurea material is a high-strength, high-toughness material with urea bonds formed by the reaction of isocyanates and amine compounds. It has characteristics such as rapid curing, 100% solid content, environmental friendliness, non-toxicity, high wear resistance, and high impact resistance. It is widely used in bridge anti-corrosion, building waterproofing, industrial anti-corrosion, transportation equipment, and special scenarios (such as nuclear power) to significantly extend the life of substrates.

Polyurea materials are diverse, with more common types including aromatic spray polyurea (first generation), aliphatic spray polyurea (second generation), and aspartic polyurea (third generation polyurea).

Among them, aromatic polyureas are formed by the reaction of aromatic isocyanates with amine-terminated compounds, featuring an extremely fast reaction rate, capable of curing within seconds to minutes. They are mainly used in industrial fields that demand extremely high material strength and wear resistance, such as industrial waterproofing, industrial anti-corrosion, and wear-resistant linings for high-end machinery and equipment.

Aliphatic spray polyurea is formed by the reaction of aliphatic or cycloaliphatic isocyanates with amine-terminated compounds, and antioxidants and UV absorbers are added. It has been improved in terms of UV resistance, anti-aging, and curing time, and can meet certain requirements for weather resistance in outdoor environments.
The third-generation polyurea - polyaspartic ester polyurea, abbreviated as aspartic polyurea, is formed by the reaction of polyaspartic esters with isocyanates. It is commonly used in areas such as home beautification, outdoor architectural decoration, vehicle coating, marine facility protection, and industrial coatings, providing reliable protection.