This block makes such a difference. Our dog fits better in a L, but it was terribly difficult to fit her in to a L. Fitting her into an XL was easy, but she sagged into the bottom of the sack in it. The block solved it, giving her a boost so there's no sag, and no drag on my shoulders. One note - on the instruction videos, I have not seen the way we get Ginger in, where the dog is lured in through the bottom and secured after buttoning the top. This was the only way that worked for our 50-pounder.