These packages of Tuna and other foods in pouches are becoming more and more common.

They are suposed to taste fresher because the thin pouches do not have to be heated as long as cans.

In canning, the product is sealed in a can and heated under pressure in a retort chamber.

In the case of tuna, a can of tuna is heated for about 4 hours to sterilize the contents. With retort pouches of tuna it only takes about 45 minutes (thiner package, transfers heat faster). The pouch tuna should have less of a "cooked" taste due to the shorter processing time. In addition, to keep the contents of a can from scorching during the longer heating period, more liquid has to be put in a can.

That's the reason that pouch tuna does not have to be drained and should taste better (at least in theory).

I still buy cans, because it is cheaper. At least right now you can by canned cheaper. The actual cost of producing canned vs pouch is about the same. Canned is cheaper now because plants already have canning equipment, while pouches involve new equipment.