Nuna LUMN vs. Nuna AACE | Car Seat Comparison
As our kids grow, car seat needs change—and the booster phase marks the final stretch of the journey. It's all about finding the right balance between safety, comfort, and independence. The Nuna LUMN and Nuna AACE are both great options for this stage, but they serve slightly different purposes. In this comparison, I’ll break down the key differences to help you decide which one is the best fit for your growing child.
Nuna LUMN
The Nuna LUMN is Nuna's first harness-to-booster (or combination) seat designed for forward-facing use only. The LUMN begins as a forward-facing harnessed seat and later transitions into a belt-positioning booster, with the harness system easily stowed when no longer needed. It’s built with the premium safety features Nuna is known for—an all-steel frame, reinforced belt path, Aeroflex™ side-impact protection made of energy-absorbing EPP foam, and flame-retardant-free materials. The LUMN also includes leatherette accents and a streamlined design that blends well with modern car interiors.
Nuna AACE
The Nuna AACE is Nuna’s dedicated high-back booster seat designed to grow with your child through the final stages of car seat use. It starts as a high-back belt-positioning booster and later converts into a backless booster for older kids. Built with Nuna’s signature focus on safety and comfort, the AACE features a robust energy-absorbing foam, side-impact protection pods, and flame-retardant-free materials. Its 3D growth system allows the seat to expand in height, width, and depth for a truly customized fit as your child grows. With its sleek design and premium finishes, the AACE offers a stylish, comfortable, and secure ride through the booster years.
Why do kids need boosters?
Booster seats are essential because seat belts are designed for adults—not kids. Children do not typically fit properly in a seat belt until they are around 4'9" (and many state laws mandate they use a booster until then). A booster seat helps position the seat belt safely across their body.
Without a booster, the lap belt can sit too high on a child’s stomach, and the shoulder belt can hit their neck or face—both of which increase the risk of serious injury in a crash. A booster lifts the child up so the lap belt sits snugly across the hips (not the belly) and the shoulder belt lies across the chest and shoulder (not the neck).
Boosters aren’t a step to skip—they’re a crucial part of your child’s car seat journey, bridging the gap between a harnessed seat and the vehicle’s seat belt.
Comparing Safety Features: Nuna LUMN vs. Nuna AACE
The biggest difference between the Nuna LUMN and the Nuna AACE is that the LUMN includes a built-in harness. It's known as a combination seat because it combines both a forward-facing harness and a booster in one. This means that once your child is ready to face forward, you can transition them to the LUMN without compromising on safety. They can remain harnessed until they outgrow the harness limits of the seat—typically around ages 6 to 8—and then move seamlessly into booster mode when ready.
The Nuna AACE, on the other hand, is designed for older, more mature riders. It doesn’t include a harness and functions solely as a booster seat. While there are height and weight minimums, the most important factor is your child’s maturity. They need to be able to sit properly for the entire ride—no slouching, leaning, or wiggling around. At this stage, the responsibility for staying safe shifts to them.
Nuna LUMN
The Nuna LUMN upholds Nuna’s strong commitment to safety with a carefully engineered design that prioritizes both protection and ease of use. It features an all-steel frame, a reinforced belt path, and the Aeroflex™ side impact protection system made from energy-absorbing EPP foam. Certified to meet the latest federal crash test standards (FMVSS 213a and 213b), the LUMN offers advanced frontal and side-impact protection. Its True Tension™ door simplifies installation by securely locking the vehicle seat belt into place—similar in function to Britax’s ClickTight® system—reducing installation errors and boosting confidence. Additional safety-focused features include push-on LATCH connectors, an open belt path for hassle-free booster buckling, and flame-retardant-free fabrics. With GREENGUARD Gold Certification for low chemical emissions, the LUMN not only protects in a crash but also supports a healthier environment for your child.
Nuna AACE
The Nuna AACE is thoughtfully designed to provide reliable safety during the booster years. It features energy-absorbing foam and built-in side impact protection pods that offer added shielding in the event of a collision. The seat’s adjustable headrest and side wings are designed to grow with your child, helping to maintain proper seat belt positioning as they get taller. While the AACE doesn't include a harness system, it relies on your vehicle’s seat belt and is crafted to position it correctly across your child's shoulder and lap. The belt guide system helps prevent improper routing, while the rigid LATCH connectors keep the booster securely in place—even when unoccupied. Like all Nuna products, the AACE is made with flame-retardant-free materials and is GREENGUARD Gold Certified, offering safety that extends beyond impact protection to include healthier air quality for your child.
Full List of Features
Nuna LUMN Features
- 5-point no-rethread harness stows away when converting to booster
- 9 recline options in both harness and booster modes when tethered
- Bubble-free recline guides confirm the perfect riding angle
- 10-position height-adjustable headrest to accommodate growth
- Machine-washable fabrics and inserts– seat pad removes separately for added convenience
- Slim design fits 3 across in most mid-sized vehicles
- Dual flip-open cupholders
- Designed for longevity with up to a 10-year life span
- Ergonomic armrests are padded for extra comfort
- All-weather micro knit fabric provides all-season comfort
- Leatherette-wrapped calf support for comfort that grows with them
- Airline approved and FAA-certified for use in harness mode
- From fabric to foam and beyond, each element is smartly sourced to be both flame resistant and contain no added fire retardant chemicals
- Greenguard Gold certified
Nuna AACE Features
- Converts from high-back booster to backless booster as your child grows
- Energy-absorbing foam and side-impact pods offer top crash protection
- Headrest offers 9 height positions and can be adjusted with one hand
- Shoulder area of seat expands automatically when headrest is raised
- Seat offers 3 depths to support growing legs
- Built-in arm rests add comfort
- Can be reclined to 8 positions in high-back booster mode
- Belt positioner and colored belt path indicators help decrease errors
- Rigid LATCH connectors offer easy installation
- Fabrics are breathable and machine-washable
- Free of flame-repellent chemicals
- Greenguard Gold certified
Comparing Specs and Dimensions: Nuna LUMN vs. Nuna AACE
Since the LUMN is a combination seat, it's going to be heavier and bulkier than the AACE. Let's take a look at all the differences:
Weight:
Dimensions:
Recommended Use:
Harness mode: 30–65 lbs; between 34" to 49" tall
Booster mode: 40–110 lbs; between 43" to 63" tall; mature enough to sit properly the entire ride
Recommended use for high-back booster: 40-110 pounds, 38-60", age 4+; mature enough to sit properly the entire ride
Recommended use for backless booster: 50-120 pounds, 38-60", age 5+; mature enough to sit properly the entire ride
Harness Height:
Head Support Positions:
Recline Positions:
Warranty:
Expiration:
How do I choose between the Nuna LUMN and Nuna AACE?
Choosing between the Nuna LUMN and the Nuna AACE really comes down to your child’s age, maturity, and individual needs.
If your child is under 5 years old, the Nuna LUMN is the clear choice. It includes a built-in harness, which is essential for younger children who aren’t developmentally ready for the responsibility of sitting correctly in a booster seat 100% of the time. While booster seats can technically be used for children as young as 4 years old (as long as they meet height and weight minimums), it’s not recommended. At that age, most kids are still too wiggly and impulsive to maintain proper seat belt positioning throughout an entire car ride. The LUMN allows you to keep your child safely harnessed for longer—usually up to age 6–8—before transitioning to booster mode when they’re truly ready.
If your child is 5 years or older, the decision becomes more personal. At this stage, some kids may be ready for the Nuna AACE, especially if they consistently sit upright, stay in position, and understand the importance of keeping the seat belt in place. Others—even within the same family—may still benefit from the added security of a harness. The LUMN gives you that flexibility: you can keep your child harnessed as long as needed and switch to booster mode later, all in the same seat.
At the end of the day, you know your child best. Think about their maturity level, how they behave in the car, and what makes you feel confident that they’re safe and secure every ride.
Why should you trust Bambi Baby?
At Bambi Baby, our decades-long commitment to quality and customer satisfaction has established us as a trusted authority in the baby products' industry. With over 40 years of experience, we have developed a deep understanding of what parents require when choosing the perfect stroller. Our expert team is dedicated to guiding you through this important decision with personalized recommendations, ensuring that the stroller you pick perfectly matches your lifestyle and needs.
Still have questions?
Bambi Baby experts are ready to connect! If you have any more questions regarding the Nuna LUMN and Nuna AACE you can reach us at cs@bambibaby.com or chat with us on our website. We would love to hear from you!
We would also love to see you in store! Feel free to visit any of our store locations in New York, New Jersey, or Miami if you prefer personalized assistance from one of our experts. We're here to ensure you find the perfect gear for your baby with confidence and ease.