The main differences between the S1 formaldehyde filter (green) and the other Xiaomi filters, purple (antibacterial) and grey (HEPA), lie in their composition and their specific targeting of pollutants.

- The green (formaldehyde) filter is designed specifically to remove formaldehyde and other harmful volatile organic compounds (VOCs) such as benzene and ammonia. It combines an ultra-dense HEPA H11 filter with high-quality activated carbon enriched with an anti-formaldehyde formula, offering 99.3% filtration of 0.3 micron particles and a large adsorption surface area for toxic gases (57,000 m²).

- The violet filter is a triple-layer antibacterial filter that targets bacteria and dust mites as well as fine particles. It contains a larger activated carbon filter than the basic filter, with organic-metallic antimicrobial technology, making it suitable for public environments and sensitive people (children, the elderly).

- The grey filter is a classic 3-layer HEPA filter with activated carbon, 99.97% effective at filtering fine particles (PM2.5, pollen, spores, viruses) and VOCs, but without the anti-formaldehyde or antibacterial specificity of the other filters. It is designed for broad mechanical and chemical filtration, with a cylindrical construction for 360° filtration.

In short, although all these filters filter out fine particles, VOCs and certain allergens, the green filter stands out for its enhanced effectiveness against formaldehyde and toxic gases thanks to its special activated carbon. The violet adds an antibacterial function, while the grey is a standard HEPA filter with good general filtration but no specific treatment against formaldehyde or bacteria.