I've been having an occasional problem with the dark slides in my 5x4 film holders, where I pull a holder out of the bag and it catches on the dark slide of an adjacent holder, causing it to get pulled up with the resultant annoying fogging of the film inside. I'm aware of some people using elastic bands, but I wanted something more robust, easier to use, longer lasting, and which would give a known amount of pull. So, I decided to make some retainers using 25mm wide elastic, and they look like this... They were made on a sewing machine but could readily be sewn by hand if needed - the sewing is just two straight bits of stitching. The tab bit at the top is what makes it easier to use - just grab the holder at the sides, pull the tab away a little to stretch the elastic, and then move the loop to one side or the other. Same in reverse when fitting (a bigger stretch works better here). There has been no instance so far of the elastic pulling at the dark slides (but I only move it a little when removing - just enough to clear the ends of the slides so that there's no drag when moving the elastic to the side). The tabs look like this from the side... Each retainer is made from 40cm of elastic. This is folded in half and a line of stitching done across the width, 6mm or so in from the end. The position of this isn't critical - just so long as it's away from the end to ensure it doesn't fray and work loose. The retainer is then turned inside out and a second line of stitching is done across the width at the desired distance. This distance is more critical - you need to find the amount of stretch that works for your elastic. If it's not tight enough, the dark slides can still be pulled up, and if it's too tight, the elastic will degrade prematurely (or not stretch enough if you get it very wrong). For my elastic, the distance was 16cm... There are two reasons to turn it inside out before doing the second line of stitching - it helps to stop the end of the elastic from fraying (ie, it's effectively a hem), and it results in the very end of the tab being thicker than the rest by two thicknesses of elastic, so you have a little lump at the end that the fingers can work against when stretching to fit and remove (so less finger pressure needed). Haven't used them in anger yet, but they feel really good. Cost was buttons - about 40p per retainer for 10 holders (4m of elastic, plus a wasted bit to work out the right amount of stretch). Some sewing machine comments... On my machine, I found that the tension needed to be increased quite a lot to get the stitching even on both sides (was getting loops on the underside). I did three passes on each line of stitching to lock everything down. Also, I use bonded nylon thread for nearly everything because I find it's very resistant to breaking - can't say whether conventional polyester or cotton threads would survive this.