August 3, 2009:
In Afghanistan, most light armored vehicles are using Slat armor (most prominently seen on Stryker armor vehicles since 2003) for protection against RPGs (small rocket warheads with shaped charge explosives). This stuff is heavy, and there have been several efforts to make slat armor lighter. The latest effort replaces the metal slats with sheets of fabric, and this works. The Tarian fabric protection from RPGs weighs half as much as aluminum slat armor, and is less than a fifth as heavy as the original steel slat armor. The Tarian armor is designed to fit the same metal framework used for existing slat armor. The exact composition of the Tarian fabric is a trade secret, but it is resistant to fire and being shredded by bullets. The big advantage of Tarian is that it prevents making smaller vehicles unstable, and putting excessive pressure on the suspension (a problem with all add-on armor.) On the downside, you can't see through the Tarian "slat armor" because it, well, has no slats. This is not considered much of a problem, in a practical sense.
There are several manufacturers of slat armor. Two years ago, armor made from aluminum, instead of steel, was introduced. This worked just as well as the steel version, and weighed over a ton less. The lighter version of slat armor, made it possible to use on trucks (both armored MRAPs, and unarmored ones), not just because of the weight, but because LROD can be bolted on, rather than welded on, as is the case with the original steel stuff. There is also Swiss RUAG Lasso slat armor that uses a special steel that weighs half as much as the original steel used for Stryker slat armor.
The original slat armor was a 2.5 ton steel cage of armor that circles the vehicle. The U.S. Stryker was the first vehicle to use it on a wide scale. Slat armor is similar to anti-torpedo nets developed over a century ago, to protect battleships in port. When an RPG warhead hits, it detonates between the main armor and the metal slats, and does little harm. Slat armor costs about half as much as ERA (Explosive Reactive Armor), and is about a third lighter, but it is unwieldy. However, in practice, slat armor works quite well, and many other types of armored vehicles, particularly armored trucks, use it as well. The aluminum and fabric versions are easier to install and remove. This makes it useful in situations where the RPG threat comes and goes.