Great question, canon armor was assembled mostly with elastic for obvious reasons, mobility. For nice tight fitting armor either use nylon or tight elastic. Something to keep in mind any excessive gaps in these areas may be mentioned at the higher levels of approval., so nice and snug is recommended. That said, this is your armor and as Glen mentioned flexibility is key when trooping. I personally use both, most torso connections I use nylon (except for the shoulders), and lower arms are elastic. This allows for a nice tight fitting armor where it needs to be and flexible in those areas.