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Soy Candle Burning Rate

Soy candles have many claimed benefits. Many of these are obvious, but others are more difficult to prove. There are no scientific studies comparing the properties of soy wax candles with paraffin candles, except for a study by K. Rezaei entitled "Combustion Characteristics of Candles Made from Hydrogenated Soybean Oil". This study showed that soy wax candles burned longer and produced less soot than paraffin candles. It found that the untrimmed soy wax candles had a slightly lower burning rate than paraffin candles, but that the trimmed soy wax candles had a 30% lower burning rate.

We compared the burn rate of a soy candle with that of a paraffin candle. We do not claim that this is a scientific study: it is just a simple experiment! We made container candles with 80 g of wax and 50 mm tea light wicks on a metal base. The picture shows the candles (paraffin on the left, soy wax on the right) at different burn times. As you can see, the soy candle actually burned out a little faster. However, this does not prove that the soy candles always burn faster, since the burning rate also depends on the wick size.

In our experiment, the wick size of the soy candle tended to be larger and more split than that of the paraffin candles, even after trimming the wick every two hours. Soy wax and paraffin have about the same heat of combustion, so why would soy candles burn longer? Probably because soy candles burn with a smaller flame. Soy wax contains larger molecules with lower volatility, resulting in less flow of melted wax through the wick.

During this experiment we noticed something special. After cooling, the surface of the soy wax was convex while the surface of the paraffin was concave! Perhaps this characteristic can be used to distinguish between the two types of wax!