Across much of Europe the first meaningful frosts of the season have arrived just as the football calendar moves into a critical period of league fixtures and heavy training loads. At this time of year, having surfaces that stay safe and playable in all conditions is essential for equity and access to the game. However, turf is not one single material, and different systems respond very differently to cold and wet weather.
Polymer based systems and stability in the cold
Traditional rubber filled systems use SBR performance infill combined with typically PE fibres. Both are hydrophobic polymers with very low glass transition temperatures, well below -40°C. This means they remain flexible and elastic at typical winter field temperatures. The rubber granules continue to move and deform under load, maintaining shock absorption, traction, etc.… even when air and surface temperatures drop below freezing.
PurePT, a fibre based and non-filled system, behaves in a similar way. Its structure is defined by densely packed fibres. The polymer remains elastic and does not bind water, so the surface response stays the same when hot or cold.
Mineral infill systems and when sand starts to lock
Sand or mineral infilled systems behave very differently. The infill is made up of hard, angular mineral particles with pore spaces that retain moisture between the grains. As temperature falls and the surface becomes cold and wet, several things happen at the same time:
- Water between sand grains becomes more viscous and then begins to freeze
- Thin water or ice films and capillary bridges form between particles, which increases inter particle cohesion and friction
- The sand changes from a free-flowing granular material into a much stiffer, partially locked matrix (this is how we make sandcastles!)
The result is a surface that deforms less under load and absorbs less impact. In practical terms, mineral infill systems which sit comfortably inside preferred norms at warm temperatures can quickly move outside the safe or preferred ranges as they become cold. Surface hardness increases, shock absorption is reduced and the traction or grip significantly drops.
Polymer biased systems, in contrast, remain within target windows over the same temperature change because their elastic response is not governed by changing conditions.
Change in SA (%) with temperature
In the graphs this is very clear. From 23°C down to 3°C the performance curve for the sand or mineral system drops away from the green (FIFA) range of preferred values from both grip and shock absorption, while rubber filled and Pure PT systems remain stable.
This is a useful reminder that if we care about equal access to safe football throughout the cold winter months, we must design and test our surfaces for real world conditions.
