There's no escaping that the Mizuno Sky Prime is a heavy shoe. It's heavier than similarly cushioned options like the ASICS GEL-SLOWCUSH and even more cushioned shoes like the Saucony Paramount Max, and it's very noticeable on foot.

The Mizuno Sky Prime uses a dual-foam setup, with a softer PEBA layer directly beneath your foot and a firmer EVA layer underneath. There's more PEBA through the forefoot and more EVA in the heel, so the front of the shoe is softer, more energetic, and more cushioned than the rear.

The Mizuno Sky Prime uses standard flat laces with a moderate amount of stretch. They kept the shoe securely locked down throughout our testing.

Pros

Cons

• Sub-par overall energy return gives you little help through stride.

• Poor heel rebound makes rearfoot landings feel especially flat.

The forefoot delivers adequate energy return, with more PEBA concentrated through the front of the shoe, giving you a reasonable amount of rebound through toe-off and noticeably more spring than at the heel.

The heel returns energy poorly. There's more of the firmer EVA carrier foam in this area, so rearfoot landings feel muted, with very little rebound into the next stride.

Pros

• Very broad outsole gives you a supportive platform from landing to toe-off.

• Gusseted tongue keeps your foot securely locked in place.

Cons

• Soft forefoot can feel less secure under load.

The heel strikes a good balance between softness and firmness. With more of the firmer EVA carrier foam concentrated here, landings feel plush without becoming overly wobbly.

The forefoot is very soft, which aligns with the greater amount of PEBA in this part of the midsole, giving you a softer feel through toe-off, though it also means the front of the shoe doesn't feel as planted as the heel.

The Mizuno Sky Prime uses a fully gusseted tongue and has no plate. The gusseted tongue helps keep your foot securely locked in place, while the lack of a plate keeps the shoe approachable for easy running and routine miles.

Pros

• Heel provides excellent impact protection.

• Forefoot impact reduction is outstanding.

• Cushioning holds up amazingly over long distances.

Cons

The heel provides amazing cushioning overall, absorbing a large amount of road impact across different forces. It scales well as more force is applied, so heavier runners or anyone running quicker are well shielded from the road.

The forefoot cushioning of the Mizuno Sky Prime is outstanding overall. It absorbs a huge amount of road impact and continues to protect your legs amazingly, even under the highest forces we test.

The Mizuno Sky Prime's cushioning holds up excellently over our simulated 50 km long-run test, keeping your legs very well protected even beyond the marathon distance. Its performance is very similar to the ASICS GEL-SLOWCUSH and a bit better than the Brooks Glycerin Max 2.

Pros

Cons

• Limited airflow can leave your feet sweaty on hot or long runs.

• Absorbs a lot of water, making a heavy shoe even heavier.

• Takes almost two days to dry after getting soaked.

The breathability of the Mizuno Sky Prime isn't bad. There's some airflow through the upper, but your feet can still get hot quite quickly on longer runs or warm days.

The Mizuno Sky Prime takes almost two days to dry fully. Even if you stuff it with newspaper and leave it in front of a fan, it's very unlikely to be completely dry for your run the next day.

The Mizuno Sky Prime has acceptable water absorption overall, but this is already a heavy shoe. It takes on almost half its dry weight when soaked, so one soaked shoe weighs more than a dry pair of HOKA Mach 7s.

Pros

• Forefoot has a bit of spring through toe-off.

Cons

• Low heel energy return means rearfoot landings aren't very springy.

The heel has an unremarkable amount of compression. It compresses more as additional force is applied, but combined with the poor heel energy return, rearfoot landings don't feel particularly bouncy.

The forefoot compresses decently, and significantly more than the heel. It also returns more energy, so you get more spring through the front of the shoe.

Pros

• Very good rocker angle helps guide a quick rollover.

• Decent forefoot stiffness gives you some leverage through push-off.

Cons

• Soft forefoot limits how forceful push-off feels.

• Forefoot doesn't spring back with much force as it unbends.

The Mizuno Sky Prime returns an unremarkable amount of the energy stored when it springs back. You get some assistance through toe-off, but not enough to make the shoe especially efficient.

The Mizuno Sky Prime has a decently stiff forefoot, giving you a satisfactory amount of leverage through toe-off. It's significantly stiffer than the plastic-plated Neo Vista 3, despite lacking a plate, likely because its more aggressive rocker geometry makes the front of the shoe harder to bend. That said, a plate alone doesn't determine stiffness, its shape and placement, along with the foam, also affect how the shoe flexes.

The forefoot rocker helps your foot roll forward impressively quickly through toe-off. It's more pronounced than the rocker on the ASICS GEL-SLOWCUSH and even more curved than in marathon racers like the PUMA Fast-R NITRO Elite 3, so you get a great amount of assistance when pushing off.

Pros

• Very good forefoot rocker helps guide you smoothly through toe-off.

• Heel does a decent job of moving you into midstance.

• Rocker stays stiff enough to maintain rolling motion under load.

Cons

The rocker is decently stiff, so it maintains enough of its shape under load to give you a decent amount of assistance as you roll through the stride.

The Mizuno Sky Prime has a huge stack in both the heel and forefoot. Traditionally, a max-stack shoe was considered to need more than 40 mm of foam in the heel, and the Sky Prime clears that mark at both ends, with so much foam up front that its forefoot is taller than the heel of shoes like the HOKA Mach 7.

Despite its relatively shallow angle, the heel rocker of this shoe still does a decent job of moving heel strikers smoothly into midstance.

Pros

• Length is bang on.

• Enough room through the forefoot and arch.

Cons

• Shallow toe box may cause chafing if you need more vertical room.

The Mizuno Sky Prime is a better long-run shoe than the ASICS GEL-SLOWCUSH. Both cost the same and provide amazing cushioning and hold up similarly well as the miles build, but the Mizuno is a smoother, more efficient shoe that gives you more assistance over extended efforts. It's also slightly more stable. That said, the ASICS is lighter, so it's the better option if you want maximum cushioning with less bulk.

The ASICS SUPERBLAST 3 is a better running shoe overall than the Mizuno Sky Prime. It provides better cushioning while weighing significantly less, and its much better energy return makes it far more capable when you want to run faster. It can also cover pretty much all of your training and is the better option for getting you through a marathon. The Mizuno is cheaper and much more stable, with a smoother roll, so if you just want a stable shoe for relaxed running and don't want to spend SUPERBLAST money, it's the better pick.

The Mizuno Sky Prime is a better daily trainer than the Mizuno Neo Vista 3. It's much more stable, with a smoother roll that makes it easier to settle into a rhythm on easy runs, and its forefoot provides better cushioning through toe-off. However, the Neo Vista 3 is significantly lighter and returns more energy, so it's less tiring to run in and is the better choice if you don't want a bulky shoe for long runs. Its heel is also more cushioned, making it better suited to heel strikers, and it's a great alternative if you can find it at a discount.