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Does Rubber Mulch Get Hot?

June 11, 2015

thermometer with question marks on rubbermulch

We all want our homes to have curb appeal and be made up of parts that are low-maintenance, safe, and durable at the same time. The same holds true for our gardens and landscapes. Rubber mulch is fast gaining popularity as an option for various landscaping applications given its inherent qualities. However, given its relatively new entry into the market, it has also been been met with some skepticism regarding health and safety. Chief among the concerns is whether it gets too hot, especially in the summer.

Rubber mulch has very high insulating properties and for gardens, the insulating quality of rubber is helpful to many plants because they thrive in warm temperatures. Unlike organic mulches, rubber mulch is non-porous, so water and fertilizer flow freely to the soil and plants that need them. As playground fill, rubber mulch is actually endorsed by the US Consumer Product Safety Commission for its high shock absorbency rate. The White House playground also utilizes a rubber mulch surface.

Still, what worries most parents about it is whether it gets hot enough to burn delicate skin. Under intense sunlight, rubber does get hot, but in order to get some real world data we decided to test rubber mulch against other common materials found  throughout the urban landscape.

So how hot does rubber mulch get relative to other common outdoor surfaces?  We set out with our notebook and infrared thermometer to find out.

Our testing was conducted on a bright sunny day with temperatures of 88 degrees and a UV index of 9 which is classified as very high.

Not surprisingly the rubber mulch samples measured between 150 and 154 degrees F.  Perhaps more surprisingly, we found that other common surfaces tested in a similar range. An asphalt driveway tested at 131 degrees, whereas the adjacent concrete sidewalk measured 112. Wood decking reached a temperature of 149 degrees while the adjacent wooden picnic table measured 126. A dark colored plastic lawn chair was recorded at 140 F.  The surrounding grass was considerably cooler at 84 degrees F.

While we confirmed that rubber mulch does indeed get hot under intense UV conditions, we were surprised to find so many other surfaces testing in similar temperature ranges and the question we found ourselves asking was, “why aren’t more people being burned by common surfaces at these temperatures?”

The answer seems to lie in the rate of heat transfer.  Burns begin when the skin reaches 111F which happens to be the threshold of pain.  The human response to pain of course is to distance oneself from the source and therefore most injuries are avoided simply by removing oneself from the heat source quickly.

Rubber mulch offers significant advantages over traditional landscaping and mulching materials including aesthetic advantages as well as the significant reduction in ongoing labor and maintenance, translating into a lot of savings in the long run.

In weighing the safety issues it would appear that although caution should be taken under certain weather conditions and in relation to very small children in particular, the risks associated with serious injury don’t appear to be any more significant that many other common outdoor surfaces.