A way to check if a child is ready to safely use an adult seatbelt without a booster. All five steps must be met for a safe fit - most children do not pass until around 150 cm tall. 1. The child can sit all the way back against the vehicle seat 2. Their knees bend naturally at the edge of the seat 3. The lap belt sits low on the hips (not on the tummy) 4. The shoulder belt sits across the middle of the shoulder (not the neck or face) 5. The child can stay in this position for the whole journey If any of these aren’t met, a high-backed booster is still needed, or a backless booster if they are over 150cm.

An independent European crash testing organisation that assesses car seats beyond legal minimum standards. Results include safety, ease of use, ergonomics, and more.

The support provided by a retailer after purchase. This can include help with installation, fit checks, troubleshooting, and ongoing guidance to ensure the seat continues to be used safely.

A safety feature designed to stop a car seat from tipping or spinning forward during a crash. Common examples include Support Legs (which brace against the floor) and Top Tethers (which attach to a specific anchor point).

Advanced Side Impact Protection / Side Impact Protection Specialised energy-absorbing components built into the side of a car seat shell. SIP is designed to reduce the distance between the car door and the seat, absorbing the initial force of a side-impact collision before it reaches the child.

The specific route a vehicle seatbelt must take to securely install a car seat. On most seats, these are color-coded: Green (R129) / Blue (R44) for rear-facing and Red for forward-facing. Correct routing is critical; even a small error in the belt path can lead to seat failure during an impact.

The ability of a vehicle seatbelt to pull itself back into its housing. When installing a car seat or using a High-Backed Booster, the belt must retract smoothly and remain taut. A "lazy" or "sticky" retractor can leave dangerous slack in the safety system.

The crease in the vehicle seat where the backrest meets the seat cushion. This is where ISOFIX anchor points are located and where the ISOFIX base of a car seat must be firmly wedged to ensure a stable, secure installation.

Backless Booster A booster cushion without a backrest or side-impact wings. While legally sold for children over 22kg, backless boosters offer no protection for the head or neck in a side-impact collision. Best practice is to remain in a High-Backed Booster (HBB) for as long as possible (to 150cm) and only transition to a BLB if the child has exceeded this limit but cannot yet meet the 5 step test to be without any seat.

A critical fitting error that occurs when the vehicle's seatbelt buckle is too long, causing the plastic casing of the buckle to rest against the frame of the car seat. In an accident, the frame can crush the buckle, causing the restraint system to fail.

The child’s bottom being pushed all the way back against the seat shell or backrest. This ensures the harness or vehicle seatbelt can be tightened correctly and that the child is fully protected by the seat's safety features.

This term only applies to most (not all) infant carriers. The child's bottom must be pulled down in the seat so that it is in contact with the harness buckle. This removes excess space in the harness, ensuring the child is securely positioned and cannot be ejected from the seat in a crash.

Growth charts used to track a child's height and weight compared to the national average. In car safety, understanding your child’s centile helps predict when they might outgrow a current seat and when higher weight limit seats might be essential.

A chest clip is a device that holds the two shoulder straps of a harness together across a child’s chest. In the UK and Europe, they’re not commonly used and should only be fitted if the seat originally came with one, or if it’s a crash-tested model (like the BeSafe Belt Collector/Keeper) for children who are fitted correctly in their seat but continue to escape the harness.

A position where a baby’s chin falls, or is pushed, forward onto their chest, which can restrict their airway. This is more likely in very upright seats or those with poor support for newborns and young babies. It is a safety concern and you should aim to rectify it as soon as possible.

A vehicle feature (often in vans) where second-row seats can rotate to face the rear seats (against the direction of travel). These seats are very often stipulated in the vehicle manual as not being approved for use with a child car seat, nor do most car seats have approval to be used on these types of seats.

Child Restraint System The technical and legal term for any car seat, booster seat, or specialised restraint designed to protect a child in a vehicle.

A structural safety feature in vehicles designed to deform in a controlled manner during a collision, usually located at the front and rear of the car. Unlike the rigid passenger area, these zones are engineered to bend, fold, or crumple, absorbing kinetic energy and reducing the force transmitted to occupants.

The rate at which a vehicle or car seat slows down during a crash. Safety testing aims to manage deceleration so it happens as gradually as possible, as high-speed deceleration causes the most significant injuries.

Expanded Polypropylene A type of foam used in car seats to enhance safety. It absorbs and disperses impact forces during a collision, helping to protect a child. EPP is lightweight, durable, and often used alongside other materials like EPS to provide cushioning and additional protection.

Expanded Polystyrene A type of foam used in car seats to enhance safety. It acts as a shock-absorbing material that protects a child from impact forces during a collision by compressing and absorbing energy. EPS is lightweight, cost-effective, and is commonly used alongside other materials like EPP (Expanded Polypropylene) in car seats to provide cushioning and reduce the risk of injury.

A car seat that stays in the vehicle and is suitable from 40cm (newborn) up to 105cm or 125cm.

When the vehicle seatbelt position/buckle sits too far forward of the car seat’s belt path. This can prevent the seat from being held securely against the vehicle seat, leading to an incompatible or unsafe installation. It is most commonly seen with high backed boosters, but can affect other seat types too. https://static.wixstatic.com/media/397f4f_104344343a114ac1bab594569c6f33f9~mv2.jpg

The straps that hold a child in the seat. A 3-point harness (common in infant carriers) has three attachment points (two at the shoulders and one at the crotch). A 5-point harness has five (two at the shoulders, two at the hips, and one at the crotch), which better distributes crash forces across the strongest parts of the body.

High Backed Booster A seat used once a child has outgrown their harnessed seat. Safest to be used from 105cm to 150cm. It provides vital side-impact protection and a shoulder guide to ensure the vehicle seatbelt sits correctly across the pelvis and shoulder.

The forward dropping of a child’s head when they fall asleep in the car, sometimes when they are seated too upright, unsupported or when the harness is too loose. It can also happen when the seat’s recline angle isn’t enough for their age or size, or when the seat is lacking support in the right places for the child. Sometimes all of these things can be correct but the child's head still flops forward. It may look uncomfortable but it's not a safety concern for healthy children over 6 months old.

The distance a child’s head moves forward during a crash. Lower head excursion means less strain on the neck and a reduced risk of serious injury. While this typically applies to forward-facing seats and high backed boosters due to the direction of travel, it is important to note that while rear-facing car seats offer superior protection, they do not eliminate the risk of head excursion.

A specialised insert or padded cushion that comes with some car seats designed to support a newborn's head. These are often detachable.

A category within the R129 regulation designed to improve compatibility between car seats and vehicles. i-Size seats must be installed using ISOFIX, and are designed to fit in i-Size-approved vehicle seating positions without needing a vehicle-specific compatibility check. All i-Size seats meet R129 requirements, but not all R129 seats are i-Size.

A traditional first stage car seat, designed for newborns and infants. These seats are rear-facing only and portable, offering the best protection for a baby’s delicate spine and helping to maintain an open airway.

Metal connectors built into your car’s chassis that click directly into the car seat. This system is designed to reduce the risk of fitting errors, but does not eliminate them. ISOFIX is equally safe as seatbelt installed seat provided they're installed correctly. Note: ISOFIX has a combined weight limit of 33kg for both the seat and child, so there are no ISOFIX seats with a harness beyond 23kg. For this reason, many are limited to 18kg - though each seat can vary.

Heavy-duty straps used on many Extended Rear-Facing (ERF) seats. They anchor the car seat to the floor of the vehicle to prevent the seat from rebounding. They allow seats to have much higher weight limits (up to 36kg) than ISOFIX seats. They are used in conjunction with the vehicle seatbelt and a support leg and are non-optional. Read more here(/post/what-are-lower-tethers)

A car seat designed to adapt as a child grows, covering multiple stages (for example, from toddler to booster). These seats may have adjustable features but often involve compromises c(/post/the-truth-about-multi-stage-seats)ompared to single-stage seats.

A metal pole that extends from the base of the car seat to the floor of the vehicle. It prevents the seat from tipping or rotating forward during a crash.

The standard method for checking harness tightness. Once buckled in, try to pinch the harness webbing at the shoulder. If you can pinch any fabric together, the harness is too loose and needs further tightening.

The current legal safety standard for car seats in the UK and Europe. R129 seats are categorized by a child's height and weight, must pass mandatory side-impact testing, and are designed to be more compatible with modern vehicles. All i-Size seats meet R129 requirements, but not all R129 seats are i-Size.

A sturdy bar or hoop at the foot of a rear-facing seat that braces against the vehicle's seat back. It prevents the car seat from "rebounding" or kicking up toward the rear window during an impact.

Rear-Facing / Forward-Facing RF (Rear-Facing) means the child faces the back of the car, which is the safest way to travel as the seat cradles the head, neck and spine. FF (Forward-Facing) means the child faces the front. Best practice is to delay the transition to FF for as long as possible (ideally until age 5 to 7+).

The hard, outer plastic frame of the car seat. It acts as the primary protective cage, providing the structure that holds the foam, harness, and connectors together while shielding the child from debris.

A dangerous movement where a child slides underneath the lap belt of a seatbelt during a crash. This causes the belt to ride up into the soft abdomen, potentially leading to internal injuries.

Applies to Forward-Facing seats (including High Backed Boosters) only. The critical space maintained between a child’s head and the interior of the vehicle (such as the back of the front seat) during a collision. The gap should be at least 55cm from the child's nose to the seat in front. You should aim to maximise this gap to prevent the child's head from making contact with hard surfaces.

A voluntary, ultra-strict crash test for rear-facing seats. It is the only test in the world that measures the specific force exerted on a child’s neck during a crash, ensuring forces remain below a life-threatening threshold.

Storage compartments in the vehicle floor (often in rear footwells). These may not be suitable for use with a support leg unless specifically approved, as they may not provide enough strength in a crash. Every vehicle is different so you must read your vehicle manual for guidance on whether a support leg can go on the lid, whether it needs to extend in to the bottom of the box, or if you need an approved box filler before using a support leg safely.

A strap used on some forward-facing car seats that attaches to a dedicated anchor point in the vehicle (usually behind the seat). It helps reduce forward movement of the seat in a crash and improves stability. Top tethers are sometimes also used on rear-facing seats, but this is less common as they can limit movement, reduce recline options, and make installation less flexible.

The organisation behind the Swedish Plus Test. VTI conducts some of the most stringent crash testing in the world, focusing on forces placed on a child’s neck.