Trimethylsiloxysilicate, often referred to as MQ silicone resin in cosmetic ingredients, is a crucial "hard film" forming agent in sunscreen products. Its core value lies in the fact that it can significantly enhance the durability, water resistance and user experience of sunscreen products through its unique film-forming mechanism. 
Constructing the "hard skeleton": Trimethylsiloxysilicate can form a dense, breathable and hydrophobic film on the skin. This film is like a sturdy framework, providing a stable attachment base for the sunscreen agent. It can effectively resist sweat, water flow (waterproofing), and daily friction, preventing the sunscreen components from being easily rubbed off or washed away. 
Collaborative soft film, combining hardness and softness: When used alone, the formed film might be too hard and prone to cracking. Therefore, in modern formulations, it often works in conjunction with "soft film" components such as acrylic polymer. The soft film provides flexibility and adhesion, and the combination of the two forms a strong, adaptable, and skin-fitting composite film. This ensures long-lasting protection while avoiding a tight and cracking sensation. 
Enhanced protection and skin feel: This composite film helps the sunscreen agent distribute more evenly and stably on the skin surface, reducing the protective gaps caused by component migration. Research has confirmed that this synergistic film-forming system can significantly enhance the product's sun protection index (SPF) and the protection effect against long-wave ultraviolet rays (UVA). At the same time, its silicone resin properties give the product a smooth application feel, and after film formation, it presents a refreshing and non-greasy skin feel. 
In summary, trimethylsilyloxy silicate is not merely a thickening agent. Instead, it is a key technical component that fundamentally enhances the durability, protection efficiency, and user experience of sunscreen by constructing a hydrophobic, anti-friction hard membrane and assembling it in synergy with the flexible components.