Yes, your hot tubs do need covers! Not only are they essential to protect the water from leaves, animals and debris, but they help keep it warm, lowering your energy bills.
Look for hot tub covers that are light-weight, energy-efficient and highly insulating, between 3 and 6 inches in thickness;
Go for a thicker cover if you live in an area that gets a lot of snow, as it will need to withstand its weight during the harshest winters;
If you have particularly curious young children, you might want to consider lock straps, too;
Some covers can be quite hard: if you think you'll struggle to move yours, make your life easier by purchasing a hot tub that comes with a cover lifter.