I needed a bag for transporting the equipment for my hobby - horse riding. It had to be insensitive to dust and dirt (=> grey color and synthetic leather), insensitive to humidity from outside or inside (=> oil cloth inside) and I wanted to have some inside pockets for a bit of order in my stuff.
At first I over-sized the bag a little. It had been all sloppy and unhandy, so I ripped it up and cut the pieces smaller. Now it is maybe a little bit too small, but still acceptable, even when the helmet is not fitting in completely. Anyway there are only the most basic things inside that I like to have around.
When getting the helmet out, you see the bottom is filled with the other stuff and you can see the side pockets I made from oil cloth, but I haven't the impression, that they are helping much for the tidiness.
I am not entirely happy with it, but I will try out this evening if the bag is at least fulfilling the needs of transporting my stuff in one hand and not forgetting something ...