An F1b Labradoodle is the result of two generations of breeding. In the first, a purebred Labrador retriever is bred to a purebred poodle to produce an F1 Labradoodle. In the second, an F1 Labradoodle is bred to either a pure Lab or a purebred poodle to produce F1b Labradoodles.
"Back breeding" is the term used when an F1 crossbreed is bred back to a purebred from either of the two breeds used to produce it. On average, F1b puppies have 75 percent of their genes from the breed used for the back breeding and 25 percent from the other parent of the F1 dog. Breeders use back breeding to select for desired traits found more often in one or the other of the pure breeds used in the original cross.