F1 means first generation...Which is a maltese purebred or a cavalier purebred bred to a poodle.  F1B means second generation.  A Maltipoo mix breed or Cavapoo mix breed bred back to a purebred poodle or a purebred maltese in the case of a maltipoo or a cavalier in the case of a cavapoo.  My F1B cavapoos are always bred back to a poodle never a cavalier.  This is to offer more of a hypoallergenic breed.   I offer mini and toy size cavapoos.  A mini cavapoo is a cavalier bred to a miniature poodle.  A toy cavapoo is a small cavalier bred to a toy poodle.  Same goes with a mini or a toy size maltipoo.  I focus on the toy size maltipoo with a weight range of 6 to 10 pounds.  Mini cavapoos are 12 to 15 pounds and toy cavapoos are 8 to 12 pounds...