Disposable paper tea filter bag. You can load the desired amount of tea, fold back and close with a clip.
For single use only.
XS size (6x13 cm), where you can fill enough tea for one mug, about 2-5 dl.
The price is for a box of 100 paper filters.
A practical Youtube video shows the use of the XS tea filter for teapots here: XS Teafilter