Poly Tarp Construction:
Poly Tarps are typically made of multiple layers with a woven,
mesh fabric sandwiched between two or more polyethylene sheets.
Polyethylene is the same material used in cables, pipes, and molded
containers. It accounts for the largest portion of recycled plastics
(recycle codes 1, 2, and 3). There are many other features that should
be considered as well when evaluating your purchase. Consider the following
list of tarp features before deciding on the right tarp for your application.
* Tarp Thickness - This is the actual thickness of the tarp measured
in mils (1/1000 of an inch). The larger the number, the thicker the tarp.
Typical lightweight, blue tarps found in most retail or hardware stores are about
6 mils. If you are planning a heavy duty use, such as covering a carport,
consider a heavy duty tarp at 11 to 12 mils or a super heavy duty tarp at 23 mils.
* Size - The specified sizes of poly tarps may not be the actual measured
size. Tarp sizes will vary from one manufacturer to another. Be sure to check the
description of the tarp. Tarps will typically be 4 to 6 inches smaller in each
direction than the specified size. If a tarp is specified to be 10 feet, the actual
size will be 9 ft 6 in to 9 ft 8 in. This is due to the fact that tarps are cut to
size and then hemmed at the edges. The hem uses up some of the original width
leaving the tarp slightly smaller than specified.
* Lamination - Most poly tarps are constructed with a mesh fabric laminated
between at least two layers of polyethylene film. Some heavy duty and super heavy
duty tarps will have an additional layer of black polyethylene laminated in the
center to prevent sun rays from penetrating the tarp.
* Mesh Fabric - The mesh fabric specification is the number of threads per
square inch. An 8X8 mesh count would mean 8 threads per inch in both the horizontal
and vertical direction. Heavier duty tarps will have from 12 to 16 threads per inch.
The thread weight may also be specified in denier. Denier is the weight in grams of
9000 ft of thread. The larger the denier, the heavier the thread. Denier is not
always specified, but generally the heavier duty the tarp, the larger the thread.
* Grommets - Grommets are metal rings lining a small hole at the edge of a tarp
to accommodate the attachment of cords or bungees to the tarp. Spacing of grommets
will vary from 18 inches to 36 inches depending on the grade of the tarp. Higher
grade tarps will have the grommets spaced approximately 18 inches apart. Grommets may
be made of aluminum (rust proof but not the strongest), brass (rust proof and strong),
or plated steel (rust resistant and strong). The most durable and rustproof grommets
for outdoor use are brass.
* Reinforcement - Tarps may have additional reinforcement around the perimeter
of the tarp to help prevent ripping and tearing. There are four main types of reinforcement.
o Corner reinforcement - The higher the grade of tarp, the more likely you
will find heavy reinforcement in the corners. Corner reinforcement helps prevent
tearing out of the corner grommets and will extend the life of your tarp.
o Perimeter rope - This is a rope which has been sewn inside the hem at the
edge of the tarp to add reinforcement strength to the tarp.
o Hem - The hem is formed by folding the edge of the tarp back onto the tarp
and then stitching the entire hemmed area. Most poly tarps have a hem.
o Grommet reinforcement - In addition to the corners some tarps have additional
reinforcement at each grommet sometimes called a patch. This reinforcement is added
to the hem area of the tarp and is typically only available in the heaviest duty tarps.
Note that some heavy duty tarps may use additional reinforcement in the hem to improve
grommet strength and will not have the perimeter rope.
* UV Treated - This is a chemical treatment done when manufacturing the tarp to
help protect degradation of the poly tarp from UV rays.
* Waterproof - Most poly tarps are waterproof. The laminated film layers of
polyethylene are naturally waterproof. However, some screen poly tarps designed for
truck bed covers and sun screens are not waterproof.
* Mildew and Rot Resistant - Since polyethylene is water proof it also is very
resistant to rot and mildew.
* Flame Retardant - No poly tarp is flame-proof and should not be used near open
flames or other heat sources. Some flame retardant tarps are available. If you are
purchasing a flame retardant tarp, be sure you know and understand the specifications.
* Sun Blocking - Sun blocking tarps have an additional layer of black
polyethylene and black mesh threads to form a light blocking tarp.
* Color - Tarps come in a wide range of colors all of which will not be
covered here. Some tarps have special features that may be required for your application.
o Silver Sun Blocker - These specialty tarps are designed with black
polyethylene and black mesh laminated between silver poly on one side and either
a light or dark poly on the other depending on the manufacturer. The key feature
of these tarps is that they block the sun light, and are cooler underneath in the
summer. These tarps are great for canopies and carports.
o White - These tarps are great in that they provide some shade but allow
some natural light to come through. Applications include wedding receptions, dining
canopies and vendor booths.
o Clear - Clear poly tarps are great anywhere you need to have a lot of light
but still need to have protection from the weather such as green houses.
o Blue, Green, Brown - These tarps have no special color features but are
great utility tarps for use in general construction or landscape maintenance.
o Orange, Red, Yellow - These brightly colored tarps are used where high
visibility is preferred.
Special Canopy Tarps
Specialty poly tarps are tarps that
are cut and sewn to
meet a special requirement. These include peak drop or end cap tarps and valance tarps.
These types of tarps have all the same features of standard rectangle or square tarps
plus they are designed for a specific canopy function.
Peak Drop or End Cap tarps - These tarps are cut to cover the peak end of the canopy.
When ordering one of these tarps it is important to know the exact dimensions of your
canopy and the style of the peak (low, medium or high). If you are designing your own
canopy and plan to use an end cap tarp it would be a good idea to check out available
sizes before you start your design. They can be ordered with and without zippers that
act like a door entry.
Valance Poly Tarps - Valance canopy tarps are designed to cover the top of the canopy
frame with a flap (the valance) that hangs down over the side by 8 - 10 inches giving
a cleaner and more finished look to a canopy. Side tarps and end cap tarps can be tucked
up under the valance to provide more protection from rain. The sizing on a valance tarp
is for the main part of the tarp, not accounting for the valance portion. Actual sizes
on valance tarps are typically short by 2-4 inches of specified sizes in both directions.
Valance tarps are not recommended for use with low peak canopy designs as they do not
have enough slope to guarantee water run off over the frame edge. If used on low peak
canopies, there is a risk of water accumulating on the top of the canopy causing either
tarp damages or collapsing the canopy frame.
Replacement Tarps - Replacement of existing canopy tarps is common since canopy frames
outlast tarps. Many retail stores that sell canopy kits do not sell replacement
tarps or you may want to get a higher quality tarp. Ordering a replacement tarp is easy
Poly Tarp Comparison Table:
This table is intended to provide a quick comparison of typical tarp features.
It is not based on any known document or specification but was compiled from many
online sources. Use this as a guideline not as an actual specification.