There is a way to close your Workout Sandbags securely
and leakproof but be able to sometimes open them and change the amount
of sand in them. Do not read this as a suggestion that you use your
bags as quick-change bags. I do not think fitness sandbags should be
used that way. Just get 2 or 3 sizes and vary the reps you do to vary
the resistance. Life is short, and so should your workout be short. We
don't have time to mess with changing inner bags of sand. These steps pictured and described below are to be done after the proper amount of sand is put in the contractor bags AND the excess air is pushed out of the bags. I still think that folding it flat and duct-taping it shut is the best way to go, but this is a way to try out your first load of sand and see if you want more or less sand in the bags. Again, keep the bags loose to maximize the shifting sand effect. There is some leeway in how loose you can fill them.
Then you can twist up the contractor bags into a sort of "pony tail" after you fill it with the proper amount of sand. Push out the air and twist the bag up until it makes the pony tail all the way to the end of the extra inner bag. See the photo to left.
Then you fold the twisted part of the pony tail down some onto itself. See photo to right.
Fold the twisted up pony tail down another time.
Fold the twisted pony tail up one last time to where it contacts the inner bags with the sand in them. Be sure you have squeezed out the excess air.
Put the large rubber band that came with your bag around the folded down pony tail once.
Double up the rubber band to be tight around the folded up part of the pony tail of the inner bags.
Close up the hook and loop and you are ready to go! Here is a great page of sandbag workouts and exercises.