Nylon tea bags are tea bags or sachets that are made out of a nylon mesh.
Nylon tea bags are used primarily because they offer the potential for superior flavor, relative to traditional paper tea bags;
however, there are environmental concerns associated with their use.
https://www.teabagfilter.org/fabric-net-cloth-mesh-cloth-mesh-fabric/tea-bag-mesh/nylon-mesh-pyramid-tea-bag.html