Outcrossing with English long-wool breeds and selection, produced a well-defined breed , differing in several important points from the original Spanish merino. The size was greater with full grown ewes weighing up to two hundred pounds and rams up to three hundred pounds, live weight. The wool clips were larger and the wool length had increased to greater than three inches.
In 1889 the Rambouillet Association was formed in the United States with the aim of preserving the breed. It has been estimated that 50% of the sheep on the US western ranges are of Rambouillet blood. Rambouillet stud has also had an enormous influence on the development of the Australian Merino industry though Emperor and the Peppin Merino stud.
The fleece was valuable in the manufacture of cloth, at times being woven in a mixed fabric of cotton warp and wool weft, known as delaines.
The breed is well known for its wool, but also for its meat, both lamb and mutton. It has been described as a dual-purpose breed, with superior wool and near-mutton breed characteristics.