About 3 months ago Lian Li was teasing enthusiasts about an upcoming open air chassis series, stressing that the final designs were still in the works and calling on their supporters to offer ideas. A few months later, we have the culmination of that feedback with finished versions of the company's new O series.

The design has changed quite a bit, and from my perspective these are no longer open air cases, even though Lian Li is still classifying them as such. Instead, I would say the 'O' stands for "oversized window," as one of the key aspects of the series are the oversized tempered glass windows that combined with Lian Li's renowned aluminum construction and PCI riser cards make them perfect for showing off your machine's guts. In fact, Lian Li takes it a step further and suggests you hang these on the wall, and includes mounting holes for that purpose.

There are four new 'O' models in the series: the PC-O5, PC-O5S, PC-O6S and PC-O7S. All are based on the same design, differentiated by their size. The smallest of the bunch is the PC-O5, a Mini-ITX version that shrinks the design down to the smallest possible footprint. The larger version of the PC-O5 is called the PC-O5S which is what we are reviewing, and although the naming scheme is very similar, the cases aren't.

The PC-O5S is 19% longer and 11% taller than the standard PC-O5, while the width remains the same. It is almost 20% heavier as well, largely due to the fact that it comes loaded with three times as many fans.

Cooling is the key upgrade of the PC-O5S, as its larger size allows for dual 120mm fans on top, and with that 240mm radiator support. Along with the PC-O5 cases Lian Li also created the PC-06 MicroATX version, followed by a full size ATX version in the PC-07.

PC-O5S External Design

The Lian Li PC-O5S is large for a Mini-ITX case, though not overly so for a Mini-ITX case designed to handle high-end gaming hardware. Covering a 465 x 384mm area when lying flat, it does have a relatively large footprint but it's very thin at just 148mm. The PC-O5S has been designed so it can either lay flat or stand on its side.

Alternatively, the case can also be wall mounted, making for some high tech art work. The talking piece of the PC-O5S isn't the façade but rather the huge side panel which has been made from a sheet of tempered glass. This is what makes the case so appealing as a wall mounted object.

The case is largely made of aluminium so I was surprised to learn that is weighs 6.40kg. That was until I realized how heavy that sheet of tempered glass is.

Looking at the PC-O5S in more traditional terms, the brushed aluminium front panel is largely dominated by a massive air vent. There is also a slim optical drive slot and a small I/O panel which features two audio jacks, a pair of USB 3.0 ports, and a power switch.

The large air vent and I/O panel are cut out with sharp angles, giving them an aggressive look. Around the back the aggressive angles continue and the cut outs for the motherboard's I/O panel and expansion cases look very cool.

The right side of the case features another large vent, but behind this one are a pair of 120mm case fans. The opposite side panel is solid so there are no features to speak of here.

Underneath there are a pair of wall mounting brackets which are covered up by grommets out of the box. There is a large square panel which can be removed using four thumb screws giving users access to the backside of the motherboard tray. This panel also features room for a 120mm or 140mm exhaust fan and it might even be possible to squeeze in a small radiator here as well.

The tempered glass panel is also locked into place using four large thumb screws, making it quick and easy to remove. The 5mm thick glass panel has been given a brownish tint and is quite heavy.