The Physics of Tensile Friction & Mechanical Knot Tightening
When you pull a hairbrush straight down from roots to ends, the bristles collect small, loose micro-tangles and push them downward. As these micro-tangles collide, they interlock like microscopic hooks and eyes, compressing into a dense, tight bird's nest knot near the mid-lengths.
Continuing to pull the brush downward exerts tensile stress exceeding 250 megapascals, snapping the hair shaft at its weakest point. Bottom-up detangling isolates the ends: you release the lowest tangle first, meaning there is zero compounding friction as you work your way up toward the roots.
The Wet Hair Elasticity Trap
When hair is wet, its hydrogen bonds are temporarily broken by water molecules, increasing its natural elasticity by up to 30%. However, this also reduces its breaking load by half.
Ripping through soaking wet hair stretches the keratin cortex past its plastic deformation threshold, permanently damaging the cuticle scales. Always mist generously with a high-slip leave-in spray (like Oribe or Ouai) and use a flexible-bristle brush (like Tangle Teezer) that bends before the hair can snap.