STAYS DURING THE ENTIRE RUN! Soft, stretchy, fits my Galaxy S9. I have to remove the case and worry about the zipper rubbing the back of my phone, but I haven't noticed any scratches. It's a little difficult to get your phone out of the zip pocket while running, but not critical. It says it's weather resistant, but sweat definitely gets in the pockets. I wear size 0, xs fits perfectly. Overall, it fits my needs perfectly!