Most spearguns are powered by large latex bands. There are many options for band sizes for both thicknesses ranging from 9/16” (14mm) to 3/4″ (19mm) with both regular internal diameter (ID) and small ID. Most brands are designed to stretch to 350%. This means that the optimal band length for a speargun is the distance from the band slot to the loading notch times two (the bands go on either side from the muzzle) then divided by three and a half (the stretch ratio). (Distance x 2)/3.5 = Optimal Band Length.
Each thickness of band has an optimal amount of energy it is capable of storing. 9/16” (14mm) bands are capable of storing approximately 90lbs of force per band, 5/8” (16mm) are capable of storing approximately 110lbs of force per band and so on. Range on a speargun is largely determined by the length of the speargun, where power(penetration) is mostly determined by the number of bands.
Latex degrades over time, but some things impact it and cause it to degrade even more rapidly. Other than some chemicals, like petroleum, the greatest impacts to bands are temperature and sunlight. Bands should not be exposed to high heat. Storing your bands in your hot garage may be what makes your wife happy, but your bands are suffering for it. Sunlight is also a major impact, which mostly happens out on the boat. The best way to prevent sun damage is to keep them covered with a Neptonics Band Cover. These also help prevent abrasion and punctures of bands, and keep your spearguns organized in transit.
There are many myths about how to store bands when they are not in use. The biggest myth is that you should keep your bands in the freezer. This is not a good idea once they have been in the water. Once bands have been submerged and exposed to pressure, water pushes past the wishbone knots and goes into the inner tubing. Water crystalizes and expands when it is frozen which causes small abrasions inside the bands and actually causes them to degrade quicker. Refrigeration is a better option than freezing. Simply keeping them in a climate-controlled location away from sunlight will also ensure an extended life for your bands.
With all that being said, most speargun bands will degrade in about eight months to a year whether they are used frequently or not. Increased use will cause them to degrade more rapidly, although the argument could be made that that is a good problem to have. If you are getting out frequently, you may have to replace your bands every six to nine months. It is pretty easy to identify when your bands are nearing the end of their useful life. They will either be gummy to the touch, which is a result of significant exposure to fuel, sun or heat. Or, they will show signs of aging near the wishbone where they will begin to crack. Once you start to see these signs it may be time to look at replacing your bands.