Seedlings are made from cuttings or seeds. In both cases some principles are the same. In order to enable the seedlings to develop a healthy roots system there must be a good contact between the substrate and the seed/cutting. Therefore it is usually recommended to use a substrate with small size particles. Roots development also requires air capacity.

Pelemix ¹/₆" Cocopeat and ¹/₄" Cocopeat provides the rare combination of those two characteristics.

In addition the seedlings can not be fertilized like a regular plant because such a thing might prevent roots development.  The amount of fertilizers applied in seedling production should be done with a lot of caution.

Some seedlings growers use mixes of Cocopeat with others material like peat or perlite to get  specific characteristics of the growing media.