Colloids contain larger insoluble molecules, such as gelatin; blood itself is a colloid. Colloids preserve a high colloid osmotic pressure in the blood, while, on the other hand, this parameter is decreased by crystalloids due to hemodilution. Another difference is that crystalloids generally are much cheaper than colloids. Colloids have large particles in them so they are not as easily absorbed into the vascular bed. Because of this property colloids are used to replace lost blood, maintain healthy blood pressure , and volume expansion.