rice pouch?

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Hi all! I'm new to sewing, and I'm having a bit of a problem. I'd really like to make one of those rice heating pads with the separated areas for the rice. However, I'd like to make a 3D tubular rice pouch with separated areas. I am having a hard time figuring out how to do it, because I want it to look like a nice tube with no seams. Really, I just want something 3D and kind of rigid. See pathetic, badly-drawn diagram below.



I don't know how to do this, though. Does anyone have any ideas or resources? Thank you!