This is a raw, professional-strength developer meant to be mixed with a separate permanent color or bleaching powder, not applied by itself. At 40 volume it's the strongest option in the Hi-Test range, capable of lifting hair up to four levels, so it's intended for stylists and experienced colorists performing significant lightening work — such as high-lift color, balayage, or foil highlights — rather than casual at-home color refreshing or direct scalp use for major lightening.

Choose the 40 volume specifically when a color service calls for real lift — several levels of lightening rather than a subtle shift — since it's the highest-oxygen-release developer in the Hi-Test line and the lower volumes simply won't get there. That extra strength is also why it demands more care: precise mixing ratios, controlled timing, and generally more experience than a low-volume developer would require.

Mix strictly according to the ratio and processing time specified by the permanent color or bleaching powder brand being used — don't use a generic ratio, since this varies by product line. Patch test at least 48 hours beforehand. Wear gloves and a protective cape, and avoid unnecessary scalp contact when using it for high-lift or off-scalp lightening. Monitor processing closely to prevent over-lightening or damage. Close the cap immediately after use and store away from direct sunlight.

Pros:

• Strongest lift in the Hi-Test range (up to about four levels) for significant lightening in one process
• Thick, stabilized cream formula stays where applied and mixes to a consistent texture
• Made in Quebec and lab-tested for stable, repeatable results

Cons:

• Higher risk of dryness and breakage than lower volumes if ratios or timing are off
• Not intended for direct scalp application in high-lift work; off-scalp/foil technique is generally advised
• Requires exact adherence to the paired color or lightener brand's ratio and timing instructions rather than generic use