Just a few touches can mean the difference between old and a vastly improved design. On the left is the traditional coffee filter.
The part where the coffee powder is put (1) fits very tightly into the lower container (2), into which the decoction percolates. The lid (3) also fits very tightly over (1).
The practical problems with this design are: when boiling water is poured into (1), both the upper and then the lower containers (1 and 2) become very hot, and it is very tough to separate them unless one waits for the whole filter to cool. Similarly, the lid (3) falls off unless it is tightly fitted, in which case, it's very tough to open it in case one wants to get a second "pour" and wants to fill it again with boiling water.
On the right is a Vietnamese coffee filter, which solves these problems very elegantly. There is only one container (4) into which one tamps the coffee powder; it sits on any glass or tumbler, without being wedged tightly into it. It has two little bakelite handles which allow it to be removed from the drip container, very easily. The lid also sits lightly (and not tightly) over the container and can be removed with ease if a second "pour" is required.
It can provide coffee decoction for two large cups (sorry, tumbler/davarA!) of filter kaapi, without having to struggle with hot metal! I don't know why we can't make filters like this instead of sticking to the traditional (and user-unfriendly) design. This can be adapted to all sizes of filters.