I took this with me when I had a 1.5 hour wait for a relative's doctor appt, and worked on it in the car. It securely holds 4mm beads in place in the channels; 3mm roll around and double up a bit but they don't sneak out of their channel. 6mm poofs the plastic up a bit when you snap the lid on, but they still seem ok. Anything bulkier you'll need to store in the bigger compartments - they're a nice 1/2" / 15mm deep! I wouldn't toss this in my backpack, but it's great for car travellers.