Directly from New Balance, "An innovative foam compound providing the same responsiveness and durability of New Balance foams 30% heavier. REVlite offers a lightweight ride without minimizing construction or sacrificing underfoot cushioning or stability."
My only experience with REVlite is on the 989v1 industrial work boot. The REVlite foam has a good amount of softness/cushioning while also having a good amount of responsiveness to back it up. Despite being a boot, the 989 did not feel significantly heavier than standard shoes. In my limited experience with the technology, can vouch for New Balance's statement on REVlite.