Peptides help plump the skin by signalling skin cells to produce more collagen, which in turn firms the skin and smoothes out fine lines and wrinkles. In The Inkey List Peptide Volumizing Treatment (£10), peptides are used similarly, plumping up the cortex (the centre bit) of each individual hair strand to create overall thicker, fuller-looking hair.
Because I haven't used a hair dryer since settling into lockdown, I've tried it just as a leave-in treatment for damp hair, and I did find my hair to be considerably bouncier once it air-dried. I'll be interested to see how it makes my hair look when I finally muster up the energy to pick up a blow dryer again.