Cars & Other Vehicles Is Ultraboost 21 true to size? Is Ultraboost 21 true to size? With that much Boost underfoot, I appreciate the secure feeling of the Primeknit upper. The fit is true to size. I almost forgot about the outsole. Continental Rubber is back with the Stretchweb outsole that is durable and grips well.2021-02-13 Related Posts:How do I make my ultra boost wider?What does Continental mean on Adidas shoes?Is Ultraboost good for heavy runners?How To Clean Golf Grips