Aluminium provides a slim profile for glass panelled bi-fold doors to create an elegant look. As far as the glass panels go, you have several glazing possibilities. Here are some standard options.
Laminated glass brings security and also other practical benefits that make a home more comfortable. It has a middle resin interlayer with a glued glass pane on either side to form a multi-layer glass sandwich. This creates a secure barrier as the interlayer typically holds the glass together if it breaks; while it might crack, the panel remains in place until help arrives. Also, because it usually stays together, flying pieces of glass don't cause injury. Particular interlayers are available, as well, that muffle noise and filter sunlight. Reducing glare will save your carpet, curtains and couch from fading.
Toughened safety glass is another option for aluminium doors. It is extremely tough, about four to five times stronger than regular glass and thus unlikely to break. It doesn't have an interlayer like laminated glass but instead undergoes a tempering process which provides both its amplified strength and safe breaking pattern. This pattern results in the glass crumbling into regular, rounded pieces if it shatters, which are unlikely to injure anyone nearby.
Low-E Coated Glass
A film on Low-E glass prevents heat from passing through this glass, which is handy if you have a wall of bi-fold doors. The Low-E coating can block solar heat from entering your home and making it too hot in summer, by reflecting it back. Or else, you can install the glass to prevent heat from escaping in the wintertime, by bouncing heat inwards. How you use this type of glazing depends on your local climate and primary concerns. Its advantage over tinted glass is that it allows light to flow through with absolute clarity while blocking heat at the same time.
Another possibility for your aluminium bi-fold doors is double glazing which insulates a home. This consists of two or more glass panes with space in between filled with either gas or air. Double glazed doors work by making it difficult for heat to travel; the heat has so many hoops to jump through. It has to pass the first pane, go through the middle space, and then get through the second pane. Each of these creates a barrier. Also, a gas (like argon gas) is denser than air, so double glazing that uses this in the interspace makes things more difficult still. Double glazing also muffles the noise, shielding a home from raucous neighbours and heavy traffic.