What is a a soilless potting mix ?
Differing types of soilless potting mixes can be bought from garden centres or nurseriesyou will find there is a variety to choose from. Coir fibre, peat, perlite and vermiculite make up the bulk.
It is made from pretty much anything but dirt. Peat is common as is tree bark, vermiculite, and perlite. There are many soil additives which have different draining water holding capabilities, different weights (you wouldn't want to plant something in just perlite or vermiculite because they are so lightweight the plant would fall over.) There's a lot if info online about what types of potting soils are best for different kinds of plants.
Exactly what it says normally made with peat or choir fiber.