Berbers (The Truth)
Berber carpets are very popular; this is in part due to the affordability of this type of carpet. The other part is that many carpet retailers are promoting this style of carpet as being tough as nails and that it will wear like iron. Truth be told, it simply is not true.
Olefin (polypropylene) fibers make up the majority of this type of carpet. (A small amount of nylon is used to add fullness).
Olefin fibers are the least resistant to the effects of gritty soils and high traffic and the abrasive properties of soils actually cut and scratch carpet fibers, which leads to matting, crushing, and a grey-dingy appearance in the traffic lanes. This is called simply means that the cuts and scratches on the fibers are refracting the light into the carpet (as opposed to reflecting light to your eyes), thus creating its own shadow effect. This is also the number one reason that Berber carpets have that worn look, even after six months.
Now for some technical stuff: since olefin is dyed while it is in a liquid state (prior to being extruded into a useable fiber) it is resistant to staining. This method of solution dyeing also allows for better color retention. Olefin is also non-absorbent, and extremely resistant to chemicals. Being non-absorbent, olefin carpets are prone to wicking. When spillage occurs on olefin carpets, the liquids pass right through the carpet and into the backings, under pad and sub-floor areas. So when you clean up a spill, it usually reappears once the area has dried. The moisture used to clean up a spill can actually cause old spills to wick to the surface along with any soil that has accumulated under the carpet.
This wicking action also occurs when improper professional cleaning (over wetting) is performed, the deep soils, simply wick back to the surface during the drying process. It is easily avoided when a technician cleans with lower psi and adds extra dry pass to ensure that wicking does not occur.
Berber carpets do require more day to day maintenance due mainly to the trapping effects of the looped pile. Soils and contaminants that are entangled within a loop cannot be vacuumed out easily. Therefore the carpet appears to be some what clean, but the trapped soils are destroying the carpet from the under side of the loops. Increased vacuuming is required, simply to maintain a Berber carpet between professional cleanings. I recommend that vacuuming be done from at least two directions, and that traffic lanes be vacuumed slowly. Always use a power-head with a rotating brush.
The best thing you can do is to consider cleaning your high traffic Berber every six months.
Olefin also has a low heat threshold, which means that it will melt at very low temperatures. Simply dragging the sofa across the carpet may be enough to melt the fibers with this small amount of friction.
Olefin also has an affinity for oils, so installing olefin near garage entries or kitchen areas is not advisable. Sadly oil is actually used during the construction needles used to punch the carpet fibers through the backing material are actually lubricated with oil. This oil is only removed from the expensive Berber carpets, and the less expensive styles do not get complete (if any) rinsing before they are shipped to a retailer. (Hmmm, nothing like adding oil to a fiber that loves oil).
Your best nylon carpets. Yes they are available in Berber style, yes they do cost nylon is more resistant to gritty soil abrasion and will last longer. The down side is that they are stainable and may loose some color over time, nothing a good protectant cannot overcome.