Here are some possibilities and how hair might be kept in place in each:
* If "b" refers to a specific hair accessory (like a bobby pin, barrette, or hair band): Then the answer will depend on the type of accessory. Bobby pins use tension to grip hair, barrettes have a clasp, and hair bands use elastic to hold hair back.
* If "b" is a typo and you meant "hair spray": Hair spray contains polymers that create a film on the hair, causing strands to stick together and maintain a style.
* If "b" refers to something else entirely: Please provide more details!
Once you clarify, I can give you a more accurate and detailed explanation.