Difference between CP and HP:
In 2006, the National Center for Biotechnology Information conducted a test to determine whether Hydrogen Peroxide whitestrips (HP)or Carbamide Peroxide (CP) gels are more effective. The results proved that while both methods were effective, the CP treatment made more significant variations from darker to lighter shading due to the concentration.
What does this mean for you?
Most whitening strips simply do not have as high of concentration of solution as gels that are applied to trays therefore the results are prolonged and less effective.