New Balance Fresh Foam X 880v15 vs Adidas Ultraboost 5X:
Which to Choose

The headline difference is the foam and the ride it produces. Adidas's Boost — a TPU-bead foam — is soft and overtly springy, with a bouncy rebound most runners notice on the first stride; it's a fun, energetic feel at easy and steady paces. New Balance's Fresh Foam X is the opposite temperament: smooth, even, and honest, taking the edge off pavement and rolling cleanly through your gait without the distinct bounce-back. If you want personality and pop, the Ultraboost has it; if you want calm predictability, the 880v15 is the smoother operator. Fit and upper are the second big split. The Ultraboost 5X uses a laceless Primeknit sock that hugs the foot for a slip-on feel, but that closed knit traps heat and runs warm on hot days, and it gives you no way to fine-tune lockdown. The 880v15's laced engineered mesh is more adjustable and more breathable, which matters on long summer miles. On the numbers, the two are closer in weight than their reputations suggest — the 880v15 is actually the heavier shoe at about 289g (men's) versus roughly 272g for the Ultraboost 5X — but the New Balance carries a taller, more cushioned platform (about 40.5mm heel / 34.5mm forefoot) against the Adidas's lower 38mm / 28mm stack. Drop is moderate on both, around 8mm for the 880v15 and 10mm for the Ultraboost, so neither forces a forefoot strike. Use case is where they diverge most meaningfully: the 880v15 is a genuine 10K-to-marathon workhorse with a fast edge near 5:00 min/km, while the Ultraboost 5X is happiest on 10K and half efforts and unhurried long runs, with its honest ceiling closer to 5:30 min/km before the dense foam starts to feel sluggish. Both wear well — the Ultraboost adds a grippy Continental rubber outsole — so durability isn't the deciding factor.