The chest wall is elastic, gradually stiffening with age. This pain is caused by a narrowing and stiffening of the urethral lumen. A central core acts as main horizontal stiffening and resisting element. The difference between low-and high- stretch elasticity is due to electrostatic stiffening and hydrophobic effects. An erection is the stiffening and rising of the penis, which occurs during sexual arousal. Calcium phosphate salts assist in stiffening bones. The spider is usually made of a corrugated fabric disk, impregnated with a stiffening resin. Metal foams are used for stiffening a structure without increasing its mass. The stiffening truss is open to reduce wind resistance. Strapless bras rely on an underwire and additional seaming and stiffening panels to support them. Stiffening laths, if used, are attached. The absorbed light leads to chain-breakage and stiffening. The lace maintaining its shape without stiffening is no longer a requirement. This helps improve ride quality on straights, while stiffening the suspension during aggressive driving. The design is faster to manufacture due to lightweight centrifugal stiffening of sails.