The authors constructed a D-shaped tracheal model with an elastic posterior wall, thus simulating normal tracheal anatomy more closely than previous models. The performance of 9-10 tracheal tube cuffs, of 2-3 different tube sizes (7.0-10.0 mm, ID), from six different manufacturers were tested in the model. Cuff residual volumes ranged from 1.78 to 27.35 ml. Cuff pressure and lateral wall pressures exerted by the cuff on the model were measured at the time a seal was achieved which just prevented leakage of water past the cuff. When a seal was achieved with a volume of air in the cuff less than cuff residual volume, wall pressure tended to be low (less than 35 torr) and cuff pressure closely approximated wall pressure. There was no relationship between cuff brands in the wall pressure required to effect a seal in the model. The authors conclude that intratracheal tubes should have cuffs with large residual volumes. This would permit some latitude in tube size selection while ensuring that a seal could be achieved before the cuff is inflated to its residual volume.