Final answer:
When the layers of the cuticle are very close together, the hair exhibits resistant porosity, making it more challenging for moisture and products to penetrate the hair shaft.
Step-by-step explanation:
If the layers of the cuticle are very close together, the hair has resistant porosity. Porosity refers to the hair's ability to absorb and retain moisture and chemicals. Hair with resistant porosity has cuticle layers that are tightly packed, making it harder for moisture and products to penetrate the hair shaft. This is in contrast to hair with high porosity, where the cuticle layers are raised or even damaged, allowing for easy moisture absorption but also a high rate of moisture loss.