At this point, all competitive curlers in Canada should be familiar with the World Curling announcement from last June about the withdrawal of specific foams in a small selection of brushes from World Curling’s approved equipment list for competitive play for the new 2025–2026 season.
World Curling came to their decision based on the outcome of brush testing in Morris, Manitoba during the Victoria Day weekend, along with feedback from the researchers on World Curling’s equipment advisory group, of which I am a member.
To a significant extent, World Curling really didn’t have a choice but to try and address the concerns first brought to their attention with a players’ manifesto that was put together just prior to last January’s Grand Slam Masters event in Guelph. The players who signed onto the manifesto were concerned that the brushes approved for competitive play this past season were too good: either they permitted additional carry above reasonable expectations, or they impacted the trajectory of a curling stone to a greater extent than they believed was in the spirit of the game.
The on-ice testing performed in Morris confirmed that some of the brushes that had previously been approved for competitive play were outside the scope of desired effectiveness as judged by the players. Consequently, with the agreement of the manufacturers involved, these foams were struck from World Curling’s approved list of competitive equipment for the new season, and the announcement was made public on June 20.
Then my phone exploded.
So how did we get here?
As a result of the original “Broomgate” in 2015, World Curling instituted three significant changes to brushing in competitive curling. They were: 1) All brush heads approved for competitive play must utilize Oxford 55 420 denier mustard yellow nylon as the brush head fabric, as it was this fabric that was tested in Kemptville, Ontario and was found to have the most desirable trade-off of minimal impact on the trajectory of a stone, versus reasonable improvement to the carry of a stone.
2) The existing rule that prohibited brushing a stone from any direction other than completely across the face of the stone was dropped, because the testing in Kemptville found that the brushing angle of attack made little difference in the trajectory of a stone. This meant that “corner sweeping” was no longer banned.
3) World Curling, based on the study results from the National Research Council in Ottawa, created a specification for the testing of foam used in brush pads. That specification contained a minimum and maximum amount of compression that a compliant brush head could have. That is, to be approved the foam could not be:
• so pliant that it would be easy for an athlete to fully compress the pad, resulting with the brush head itself being in contact with the ice, nor
• so stiff that the brush only contacted the very top of the pebble while sweeping.
The foam specification was chosen based on an underlying assumption that the brush head assembly would distribute the force produced by the athlete down the handle evenly across the full contact area of the brush pad. That assumption appears as one of the specific points in the specification document.
Broomgate 2.0 aka Foamgate
Since 2016, manufacturers of brushing equipment have developed numerous new designs to create brushes that are more effective, and weigh less, while still satisfying the requirements of the World Curling specification. But what this past season’s experience demonstrated was three main points:
• the existing World Curling specification for foam, by itself, is only tangentially related to the behaviour of a brush when used on the ice surface;
• differences in behaviour were independent of the brush head fabric, as all testing conducted by both World Curling and at the University of Saskatchewan used brush heads with the standardized Oxford 55 420 denier mustard yellow nylon fabric; and
• as a whole, new brushing products are made available in the marketplace without sufficient on-ice testing to demonstrate their suitability in actual brushing situations by competitive athletes.
Latest research
In addition to the recent on-ice testing done at Morris by World Curling, two research projects continue to look at elements of brushing and understanding the underlying physics of the sport. One of these projects concerns the study of brush heads and their construction, and the resulting pressure distribution when under load, which I’ve written about previously.
This work involves myself along with professors John Newhook, Michel Ladouceur, and Ryan Frayne of Dalhousie University. We intend to continue this work through this coming year in order to test the equipment that World Curling approved for this season, with the goal of providing some insight into what a new, improved brush specification might look like.
The second project, which I mentioned in a prior article, concerns an in-depth study of the physics of curling, including the characteristics of ice, stones, and brushing. This work is being performed at the College of Engineering at the University of Saskatchewan by Sean Maw and his research team of staff and graduate students; I am absolutely delighted to act as a consultant to this project.
Sean delivered the project’s initial findings to World Curling in August. Sean’s work is truly exciting in that his results, and the technology used to produce them, are groundbreaking, involving the use of high-magnification macro photography along with high-resolution infrared imaging that is able to discern temperature changes with individual pebbles.
The results are planned for future publication so I can’t go into details regarding the results, but I can say that Sean’s work, and that of his graduate students, give us an entirely new understanding of the physics of the sport, and particularly of the differences between ordinary brushing and “knifing”. I would like to offer my sincere congratulations to Sean, Grant Harris, Corin Acton, and Derek Elvin for making an outstanding contribution to our knowledge behind the physics of curling.
Watch for my next column in The Curling News; I’ve got some thoughts on what’s to come.