This blog post explores the secret behind the exceptional ice quality showcased at the PyeongChang Winter Olympics, detailing the scientific principles that give artificial ice a structure entirely different from natural ice and explaining the differences in conditions required for each sport.
Long ago, the Pyeongchang Winter Olympics, held in South Korea from February 9 to 25, 2018, concluded successfully amid rave reviews from numerous international media outlets. Intel utilized swarm flight technology with 1,218 drones to create a drone Olympic flag in the sky during the opening ceremony. The PyeongChang Winter Olympics mascot, ‘Suhorang,’ gained global popularity, with plush toys selling out completely in the official merchandise shops. Furthermore, this Olympics received top marks not only for its popularity but also for its records. During the 2018 PyeongChang Winter Olympics, ice sports saw three new world records and 25 new Olympic records consecutively broken. This marks the highest number of new records since the 2010 Vancouver Winter Olympics (2 new world records, 21 new Olympic records), surpassing even the 2014 Sochi Winter Olympics (11 new Olympic records). The primary reason for the daily stream of new records was undoubtedly the excellent ice quality at the venues. British skater Elise Christie and Japanese skater Nao Kodaira, who trained at the Gangneung Ice Arena and the Speed Skating Oval, also expressed satisfaction, saying, “The ice quality is really good. It feels like world records will pour out.” So how was this ice, so universally praised in Pyeongchang, created?
The ice in the ice rinks is formed in the exact opposite direction to ice that freezes naturally on lakes or rivers. First, we need to examine the relationship between phase change and density in materials. For most substances, when the temperature drops and the state changes from liquid to solid, the distance between particles decreases, increasing density. However, when water solidifies from liquid to solid, the freely moving water molecules form a hexagonal structure, creating empty spaces. This actually increases the volume and decreases the density. As the ice temperature rises and begins to melt again, most of these empty spaces are filled at the melting point. The remaining empty spaces are only filled as the water temperature rises to 4°C, and the density decreases again after 4°C. Therefore, unlike most substances, water has its highest density at 4°C.
When water cools, convection occurs until the lower layer reaches 4°C. Once the lower layer reaches 4°C, convection stops. Even if the surface water then drops to 0°C and freezes, the ice floats on top of the water. This principle explains why natural ice forms from the surface down. Applying this principle, we see that to freeze a very thick ice rink solid all the way to the floor in one go, the indoor temperature must be extremely low.
However, ice for skating rinks must be frozen from the bottom up, contrary to nature. First, cooling pipes are laid at regular intervals on the concrete floor. Next, a coolant called ethylene glycol is circulated through these pipes to lower the floor temperature to -15 to -10°C. Water is then lightly sprayed onto the surface to form a thin layer of ice. Impurities and air bubbles rise to the surface, where they are scraped off with a resurfacer. This process of freezing a thin layer, scraping, and refreezing is repeated. Once a 1mm-thick ice layer is formed, white paint is applied on top. Depending on the event, house lines or starting lines are marked. Next, a thin layer of ice must be applied over the paint to create a flat, solid surface. Lightly spraying water like rain for about 10 minutes forms a thin ice layer of about 0.2mm. While the required ice thickness varies by sport, generally, hundreds of repetitions of building up these thin ice layers are needed to finally complete an ice rink.
The reason for applying multiple layers of thin ice is to create solid ice that is less prone to cracking. For instance, if 3-4cm of water were poured and frozen all at once, the water molecules forming the ice would connect in a hexagonal structure. This makes the ice prone to cracking even from minor impacts, posing a risk of the entire rink splitting apart. Therefore, the delicate process of forming ice layer by layer is essential. This method also allows for the creation of pure ice, free from impurities and oxygen bubbles. If the oxygen concentration within the ice increases, it becomes opaque, weakens in strength, and reduces thermal conductivity, preventing proper transfer of cold from the floor cooling pipes. Therefore, creating oxygen-free ice is critically important.
Once the ice surface is complete, maintaining the optimal surface temperature of the ice, along with the humidity and temperature inside the arena, is also paramount. The required ice quality differs for each discipline—short track, speed skating, figure skating, curling—and the condition of the ice significantly impacts performance, with demanding specifications for each sport. First, the surface temperature of the ice determines its strength. Ice maintained at temperatures between -8.3°C and 5.0°C is classified as hard ice. This ice quality enables faster and smoother skating. However, the standard for this ‘hardness’ involves a very delicate and demanding condition: it must be sufficiently hard to withstand the force athletes exert when pushing off the starting line, yet not so rigid that the skate blades slip. Conversely, ice maintained at temperatures between approximately -4.4°C and 1.7°C is considered soft ice. While soft, pliable ice has the disadvantage of an uneven surface, it can absorb the impact during landings after high jumps in figure skating. Skate blades dig deeper into soft ice than into hard ice, resulting in greater friction and drag, which slows down speed.
Second, humidity levels within the arena can also affect skaters’ speeds. High humidity in ice sports causes frost to form on the ice surface, creating bumps. Skates catch on these bumps, making it difficult for skaters to control their speed. Conversely, if the arena interior is excessively dry, all the moisture that makes the ice slippery evaporates, potentially disrupting competition. Therefore, maintaining indoor humidity at an appropriate level is crucial. To achieve this, dehumidifiers that absorb humid air and moisture are installed inside the arena.
Now, let’s examine the ice conditions required for each skating discipline. Short track competition ice must be a solid surface approximately 3.5cm thick and maintained at a temperature of around -5.5°C. If the ice in a short track rink is too soft, skaters’ blades dig too deeply into the ice during cornering, preventing them from reaching full speed and significantly increasing the risk of falls. Bae Ki-tae, the ice quality manager, explained, “During short track races, water is constantly sprayed to repair the ice surface, causing it to gradually thicken. However, ice that is too thick is difficult to control temperature-wise, so we initially make it thin.” The ice thickness for speed skating competitions is approximately 2.5cm to 3.0cm, and the temperature must be maintained between -9°C and -5°C. In speed skating, good ice means fast ice. It must be sufficiently hard to withstand the force of the skaters pushing off, yet the surface must be very finely melted to allow the skate blades to glide smoothly. While both disciplines are record-driven competitions, the ice in speed skating rinks is harder because the straight tracks are longer, higher speeds are required, and there are relatively fewer situations demanding speed control during the race.
Figure skating rink ice is thicker, around 4.5cm to 5cm, and requires softer ice at a temperature of -3°C. If the ice temperature in a figure skating rink is excessively low, making it so hard that it doesn’t easily melt under the pressure of skate blades, cracks can form on the ice surface when a skater jumps powerfully and lands. Soft ice is essential in figure skating because it must act as a cushion to absorb such impacts.
The ice surface in curling arenas is called a ‘curling sheet’ and possesses entirely different characteristics from skating rinks. While a skating rink’s ice surface is typically completed in about two days, constructing a curling sheet takes anywhere from four to ten days. This is because the levelness of the ice surface is more critical in curling than in any other sport. Therefore, the ice is frozen in layers over 4 to 5 separate stages. Additionally, a process called ‘pebbling’ is performed, where small ice granules called ‘pebbles’ are sprinkled onto the ice surface. These pebbles are essential for the curling stones to glide smoothly across the ice and naturally curve inward or outward.
Ice quality becomes a major variable in Winter Olympic competitions. At the 2014 Sochi Winter Olympics, the ice was excessively soft and uneven with numerous pits, causing frequent falls among athletes. Notably, scenes of top contenders like figure skater Yuzuru Hanyu and short track speed skater Park Seung-hui stumbling on the ice were captured multiple times. The Pyeongchang Olympics learned from the Sochi Games’ lesson, where despite massive investment, ice quality issues led to poor evaluations. Through meticulous ice management throughout the entire process—including not only the precision-engineered ice surface but also installing advanced ice-making facilities for real-time ice condition monitoring and LED lighting to minimize heat—the organizers succeeded in creating a venue that earned worldwide acclaim from athletes. Given that the characteristics of the ice can determine the outcome of competitions, such a high level of rigorous ice quality management must be maintained for future Winter Olympics.
