I'm trying to create a bag of sugar with Lucid. I've created a box with the top face removed and applied a Lucid modifier as inflated. Inside the box is another box set as fluid (with fluid constraints off). I'm having trouble containing the sugar within the cloth. If I subdivide the box (bag) only a little it gives me the needed paper bag effect. But then the spacing is too large between the particles and the inner box (sugar) flows through the bag. If I increase the subdivisions of the bag, the sugar remains inside but the bag is too cloth-like and folds together.
How can I retain the rigid outer bag and at the same time keep the particles inside from flowing through the bag?