The effectiveness of semi-permanent hair dye can vary due to several factors related to the dye formulation, your hair type and condition, and the application process. Here are some reasons why some brands work better for you than others:

Dye Formulation:

Ingredients: Different brands use various ingredients and concentrations of dyes. Some formulations may include higher-quality or more potent dyes that penetrate the hair cuticle better.
pH Level: The pH level of the dye can affect how well it interacts with your hair. Hair dyes with a pH close to your hair's natural pH (around 4.5-5.5) tend to cause less damage and might work better.
Conditioners and Additives: Some brands add conditioning agents and other ingredients that help the dye adhere to the hair or improve its vibrancy and longevity.
Hair Type and Condition:

Porosity: Your hair's porosity (its ability to absorb moisture) significantly impacts how well dye takes to your hair. High porosity hair absorbs dye more easily but might also lose color faster, while low porosity hair can be more resistant to absorbing dye.
Texture: The texture of your hair (fine, medium, coarse) can influence how well the dye is absorbed. Coarser hair might need more intense dye formulations.
Previous Treatments: Hair that has been previously bleached, colored, or chemically treated might react differently to dyes compared to virgin hair.
Application Process:

Application Technique: Proper application is crucial. Ensuring even coverage, adequate processing time, and following the brand's specific instructions can make a big difference.
Pre-treatment: Washing your hair before dyeing can remove buildup that might hinder dye absorption. However, overly clean hair can sometimes be too slick for dye to adhere properly.
Post-care: How you care for your hair after dyeing, such as using color-safe shampoos and conditioners, can affect the dye's longevity and vibrancy.
Environmental Factors:

Water Quality: Hard water with high mineral content can impact how well the dye takes to your hair.
Sun Exposure: UV exposure can fade hair dye faster.
Brand-Specific Factors:

Quality Control: Some brands maintain higher consistency and quality control, ensuring their products perform well each time.
Innovation: Brands that invest in research and development may have better-performing products due to advanced formulations.
Experimenting with different brands and paying attention to these factors can help you determine which semi-permanent hair dye works best for your specific hair type and needs.