Hot tubs that are installed outdoors typically require a cover to keep the water warm when the hot tub is not in use. If you do not want use a hard cover with the hot tub you can install a floating insulation blanket to help keep the water warm. A hot tub floating insulation blanket can be purchased specifically for your hot tub or you can make one from an old pool cover.
Measure the width and length of the hot tub with the tape measure.
Spread the old pool cover on the ground and transfer the measurements to the cover. Cut the cover to the dimensions of your hot tub with the scissors.
Place the pool cover so that it is centered over the hot tub. Trace around the inside edge of the hot tub with the felt tip marker.
Take the cover off and then cut around the line you made in step 3 with the scissors. This will trim the pool cover to the inside shape of your hot tub.
Place the pool cover back on the hot tub to see how much more you will need to trim off so that it will float on the water.
Cut a small amount from the outer edge of the cover and then test the fit again. Repeat this step until the cover fits inside the hot tub and floats on the water.