“Boost” (most commonly the Adidas Boost midsole) is a cushioning foam made from expanded thermoplastic polyurethane (often called TPU or E-TPU) formed into tiny energy‑storing pellets that are fused into a single midsole. It improves running in several measurable ways:

How it works (mechanics)

• Energy return: The compressed TPU pellets deform when your foot strikes and then spring back quickly, returning a portion of the stored energy to your stride. That gives a perceptible “bouncy” or responsive feel.
• Viscoelastic cushioning: Boost combines shock absorption with a snappy rebound — it cushions impact while returning energy rather than just dissipating it as heat.
• Distributed impact: The pellet structure disperses forces across the midsole more evenly than many single-piece foams, reducing localized peak pressure on foot and joints.

Performance benefits for runners

• Improved comfort and shock attenuation: It reduces perceived impact and can lower fatigue from repeated pounding, especially on long runs.
• Enhanced responsiveness and perceived propulsion: Many runners feel a livelier toe‑off and somewhat improved running economy because less energy is lost on impact.
• Durable cushioning: E-TPU tends to retain thickness and responsiveness longer than some softer EVA foams, so shoes keep their feel over more miles.
• Good cold-weather stability: Boost maintains more of its cushioning and responsiveness in cold temperatures than many traditional EVA foams, which stiffen and lose rebound.

Practical trade-offs and considerations

• Weight and stack height: Boost midsoles can be thicker/heavier than ultralight EVA alternatives, so some models may weigh more or have higher stack heights that change stride mechanics.
• Stability: Because it’s very cushioned and bouncy, runners who need strong medial support or prefer a very stable platform may find it less secure without an upper or midsole design that adds guidance/stability features.
• Personal feel: “Bounce” and softness are subjective — some runners love Boost’s lively cushion, others prefer a firmer or more grounded ride.
• Not a magic fix: Boost aids comfort and may improve perceived efficiency, but biomechanics, training, shoe fit, and running form remain the dominant factors for performance and injury risk.

Which running uses benefit most

• Long runs, recovery runs, and daily training where comfort and reduced impact matter.
• Some racing shoes use tuned Boost for fast efforts, but elite race performance often pairs it with carbon plates or firmer foams for propulsion and stability.

Bottom line Boost works by using fused TPU pellets to create a midsole that absorbs impact and returns energy efficiently, giving many runners a cushioned yet responsive ride that stays consistent over time and in variable temperatures. Whether it improves your running depends on your preferences, gait, and the specific shoe design that uses the Boost material.