Although you need much less Techni Ice that you would bagged ice or gel ice packs, you still need to make sure you use enough to do the job. Here's what we recommend:
If you know the actual size of your cooler in litres (it's often listed somewhere on the container) then you can use the general rule of thumb of 1 sheet per 7 cubic litres of ice box.
Because Techni Ice is flexible when frozen it is easier to pack your cooling sheets in and around containers and bottles in your picnic cooler. Also, keeping in mind that cold air falls downward, when you use a large sheet (cut another sheet up into pieces for use in between objects or for small coolers and lunchboxes) in your cooler, lay it on top of everything to keep everything frozen longer.