But what is the difference between heavy duty and medium duty tarps, and when do you use them? The rule of thumb when choosing a tarp is deciding what it will be used for and, in almost all cases, if a tarp will be outdoors for an extended period of time protecting one or more objects, a heavy duty tarp is the way to go. Common objects needing a heavy duty tarp are boats, RVs, and cars and, whether suspended in a canopy or wrapped around the object and secured with bungee cords, a tarp covering these objects outside should be heavy duty, as it will need to last and protect for at least six months.

But, sometimes, a tarp isn’t needed to protect things long term. In fact, an object may only need a tarp for a few days to a week and, in this case, a medium duty tarp is appropriate. The most common medium duty tarp is a blue tarp, which is seen in many locations, although particularly during tornado or hurricane seasons in the Midwest and South. A blue tarp, when used as a roof patch, can last up to 90 days for protecting the inside of a house from water damage and other temporary outdoor uses, as well.

Every rule has an exception and, in the case of long term and temporary coverage, the exception is a baseball tarp. Although a baseball tarp is needed to cover a field in case of rain, it isn’t used consistently long term, unrolled only in case of rain or other weather, but is still a heavy duty poly tarp.

For the basic canopy for a portable garage, the basic material is heavy duty polyethylene. What constitutes a heavy duty poly tarp? A heavy duty poly tarp, as it will be used outdoors for a long period of time, should weigh six ounces per square yard and have a 12 mil. thickness, 14×14 mesh count, as 1200 denier. When used with a powder coated or galvanized steel frame, the tarp needs to have grommets, spaced every twelve inches, which can be attached to the frame with bungee cords.

Aside from the physical composition, a canopy needs to have additional properties to keep it in shape when outdoors for long periods of time. These are weather resistant properties that result from treating a tarp on one or both sides with chemicals or other protective substances. A label for a heavy duty tarp, for outdoor use, should be 100-percent UV resistant on one or both sides, tear resistant, waterproof, rot resistant, and mildew proof. In some cases, as when a tarp or canopy structure is protecting a boat or RV for at least six months, the waterproof, rot resistance, and mildew resistance are particularly important for protecting the vehicle to ensure its continued use. Other weather resistant properties a tarp should have include arctic flexibility for cold temperatures and fire resistance. For the latter, a canopy tarp should be NFPA 701, CPAI 84-7, and California Title 19 certified.

Not all tarps are heavy duty polyethylene, however, and in some cases, such as for a shade or garden canopy or a roof patch, a temporary tarp can be used, such as a blue tarp for a hurricane. A medium duty tarp, such as a blue tarp, is one example of a temporary tarp which, although treated to have the same weather resistance, the composition of the tarp is 4.5 ounces per square yard and has a 6 mil. thickness, 10×10 mesh count, and 900 denier. Another option for outdoor structures also includes mesh tarps which, although with the same properties, are made of polypropylene and allow light into the canopy shelter in a 73 shade/27 light ratio.