Linseed or Flex seed has it can also be referred too.
This Linseed filling is cleaned and graded for use has a filling that can be heated in a microwave oven or cooled in a fridge or freezer.
It’s used when a softer feel is needed has a filling in heat or cool packs.
The reason for this is that Linseed is a smaller grain and has a silky feel to the touch. So when sealed in a cloth bag it feels very smooth has it moves around in the hand. When laid on more sensitive parts of the body like the face it molds much better to the contours.
Also great to put on aching muscles or stiff necks for instant relaxation, but the cost compered to wheat can be a deciding factor if a large amount is being added to each pack.