Unicorn 3T is one of the best (maybe even the best?) grow bags for home cultivators.
The bags are made in the United States to the highest possible quality. You can fill up these bag boys with between 2-2,5 kg of substrate or spawn.
They are manufactured from polypropylene and handle sterilsation well. You can autoclave them, pressure cook them. Whatever you want for sterilisation of the substrate.
The 3T is easy to fold due to the side gussets and sport a 0,2 µm (micron) filter that allows for air exchange but does not let nasty contamination in.
The filter is tight enough so that you can use the bags for spawn but can also be used for substrates.
If you are getting started with more advanced mycological adventures, this is your go to bag!