Pre-filters are commonly made of materials that are either cheap and disposable or (more commonly) they are made of a more durable and washable material. More often than not, a pre-filter will have a very long lifespan because they are made to be cleaned, rather than thrown out. This is different than most air filters on the market, including HE Pre- filters.
One of the most common types of pre-filter looks a lot like your standard filter, and it is commonly made out of either a fabric or paper product. These filters can usually be vacuumed clean. A less common, but still very good type of filter is a grid or screen which captures larger particles out of the air. Some air purifiers may also utilize a spongy looking pre-filter which is very effective.
Fewer air cleaning units utilize a static-charged collection grid, which has one of the longest pre-filter lifetimes. These static grids work very well but are commonly a lot more expensive than the other types of pre-filters, which makes them less desirable.
Some air purifiers even utilize specialized pre-filters which may include activated carbon, which can be an invaluable extra. However, the drawback to some of these filters is that they may, in fact, need replaced.
This can result in an added expense, which may be a drawback to such a design. However, there are many air purifiers on the market which have a separate pre-filter and carbon filters. This means that you can have the best of both worlds, namely a washable pre-filter that won’t need to be replaced, in addition to a separate carbon filter.