I have found that how you insert the microSD cards makes all the difference. A gentle push to get them just below the surface of the foam, with the edges of the foam cutout just over the top of the card, seems to work for me. Alternatively, many of the microSD cards are sold with an SD card adapter that the microSD card fits inside of, allowing you to double up each foam slot, and securing the microSD card underneath and the one inside the the SD card adapter. Thin is indeed better. I found the credit card holders too hard to remove the cards from, sending them into oblivion during the recoil after release.