friability

Friability is how easily a tablet chips, flakes or crumbles at its surface when knocked about. Think of how a biscuit sheds crumbs when shaken in a tin — a too-friable tablet does the same in its bottle, arriving chipped, dusty and underweight. Friability measures resistance to this surface wear and abrasion, not to a single crushing blow.

The standard test puts a weighed sample of dusted tablets into a rotating plastic drum (a friabilator). As the drum turns, a baffle lifts the tablets and drops them repeatedly for a set number of revolutions, mimicking the tumbling of handling and shipping. The tablets are then dedusted and reweighed, and friability is reported as the percentage of weight lost. Pharmacopoeias generally regard a loss of no more than about one percent as acceptable.

Friability and hardness are related but distinct: hardness is the force a tablet survives before it fractures in one go, whereas friability is its endurance against repeated gentle abrasion. A tablet can be hard yet still friable if its surface flakes, so both tests are run together.