Fortunately, EV architectures open up possibilities to utilise a car’s footprint very effectively. With no engine to package and a simpler drivetrain, there is useful interior space to be won, but it’s an art that car manufacturers are only just starting to get to grips with.
Mercedes has done well here, because the GLB offers the same sort of leg room in the second and third rows as the much larger Kia EV9. Because the sliding and reclining second row in such cars introduces so much variability, this is quite hard to measure, but we were surprised how accommodating the third row is in the GLB. With the second row slid forwards just a bit, even tall adults are able to sit in the rearmost seats with some degree of comfort.

What helps a lot in this respect is how the seats relate to the floor. While in some EVs it can feel as if the battery is taking up a substantial proportion of the cabin height, this is not the case here. The front seats are raised on plinths, which keeps plenty of space free underneath for the second-row occupants’ feet, without making the driving position feel artificially high.
The second row also feels set adequately high to give passengers a natural seating position without affecting head room (950mm under the headliner, 1020mm if sitting further forward, under the glass roof). The relative narrowness of the cabin means it doesn’t feel quite as spacious as some, but a decently large glass area stops you from feeling hemmed in.

The third row is always a compromise in cars like these, and while in the GLB the seats are only 250mm off the floor, the cushions are sculpted to still offer some thigh support. There are Isofix points for child seats.
Sliding, tilting and stowing the second and third rows of seats is all done manually. While the lack of electrical adjustment may not sound very premium, we prefer it this way because it’s quicker. Everything is sprung in such a way that doesn’t need much muscle to move it about.
Where the GLB clearly has to concede to the EV9 in terms of space is with the boot. With all three rows up, the boot area becomes very short, with plenty of intrusion from the tops of the seatbacks. Fortunately the frunk is a useful 127 litres, though opening it requires pulling a lever.

This isn’t a seven-seater with lots of amenities, though. You will look fruitlessly for tray tables or clever storage boxes. The second row gets a pair of air vents and USB ports; the third row lacks even those.
All the way up front, the GLB is essentially a taller CLA. The seats are softer than usual in Mercedes, but are generally comfortable, with good support, although we have two gripes. The first is that the range of cushion angle adjustment is quite limited; the other is that adjustments are generally not as easy as they should be. There are basic electric controls on the door, but lumbar support is buried in the screen, as is the heating.
Multimedia

In general, the screens do a lot of heavy lifting and give the cabin quite a stark appearance; some more physical controls and warm materials wouldn’t go amiss. Fortunately, the screens respond quickly, with clear graphics and logically laid-out menus. The voice control is one of the best around, and the built-in navigation is clear and adaptable. The Burmester hi-fi in our Premium Plus test car produced a full sound.
One other feature that’s reserved for the Premium Plus is the passenger screen. Mercedes says it’s safer in a crash than holding a tablet, but apart from that we fail to see the point of it. You can play basic games on it, but this isn’t particularly ergonomic, and while it will stream media well enough, you obviously can’t take it in the house to finish the movie you started watching during a drive.
What’s a particularly poor piece of design is that the screen is visible from the driver’s seat. Using the monitoring camera for the ADAS, the car will notice if the driver looks over and will pause whatever is on the screen, which is annoying if the passenger is watching something, and doesn’t really solve the distraction issue either.