A technology controversy in the 2015–16 curling season. New brush-head fabrics, beginning with the Hardline icePad, turned out to abrade the ice surface in a directional way, which let sweepers steer a stone sideways rather than merely make it travel further. Twenty-two top teams agreed among themselves to stop using them in November 2015; World Curling imposed a moratorium; and a testing summit in May 2016 produced the single-approved-fabric rule that still governs the sport.

Was Broomgate cheating?

No, and that is the point. Every brush involved was legal when it was used, because the rules at the time said almost nothing about brush-head material. The teams using them were following the rules; the rules had simply not anticipated a brush that could change a stone’s line. The sport’s response was to write better rules, not to punish anyone.

What brush heads are legal in curling now?

At elite level, only heads approved by World Curling, using the certified fabric. Custom, modified and home-made heads are banned outright, and manufacturers submit complete heads — fabric, foam and backing together — for approval. The specification has been revised repeatedly, most recently for the 2025–26 Olympic season after complaints about over-effective foam inserts.

When did curlers stop using corn brooms?

Gradually between the 1960s and the late 1980s. Push brushes were lighter, more effective and did not shed straw onto the ice; by the end of the 1980s the corn broom was essentially obsolete in competition, though it survives as a nostalgia item and in some recreational play.

CurlTi.me/Learn/Brooms and Broomgate

Brooms, brushes and Broomgate

In the autumn of 2015 curling discovered that its brushes had quietly become steering wheels. What happened next is the best thing the sport has ever done about a cheating scandal, largely because nobody was cheating.

Last updated 2026-08-18

What sweeping actually does#

Before the scandal makes sense, the mechanism has to. Sweeping does two things, and only one of them was ever controversial.

It makes the stone go further. Brushing warms and polishes the pebble tops, reducing friction. Full-effort brushing multiplies friction by about 0.934 — a reduction of 6.6% — and that compounds over the remaining slide into several feet of extra draw.
It makes the stone go straighter. A stone that is kept moving spends less time in the slow, curling part of its journey, so sweeping a draw all the way in both lengthens it and flattens its curl.

Both of those are symmetric: they act on the stone's path as a whole. The full arithmetic is on the sweeping page. What nobody had built rules for was a third possibility — brushing that acts on one side of the stone and pushes it sideways.

Why the rules were unprepared

Because the physics is unsettled. As the curl-mystery page sets out, the leading theories all say curl comes from what is happening in a scatter of tiny contact points, and at least one says it comes from microscopic scratches in the ice. If that is true, then a brush that puts its own scratches down is not cleaning the ice. It is steering.

Corn brooms, and why they went#

For most of curling's history the broom was a household broom. Corn straw, heavy, swung rather than pushed, and loud — the rhythmic slapping in old footage is a corn broom hitting the ice, not brushing it.

Era	What people swept with	Why it changed
16th c. – 1950s	Corn-straw household brooms	It was what existed. Heavy, awkward, and it shed straw onto the ice, which then had to be swept up.
1958	The “Blackjack” — Fern Marchessault of Montreal inverts the straw at the centre of the head	A genuine improvement in durability and effect, and the last significant innovation in corn.
1960s–70s	Push brushes with synthetic heads, mostly out of Scotland	Lighter, no shedding, and — once good players demonstrated it — at least as effective. Adoption was slow because the corn broom was culturally entrenched.
By the late 1980s	Fabric-covered brushes, essentially universal in competition	Effectiveness settled the argument. Corn brooms survive as heritage items.

A modern brush is a carbon-fibre or fibreglass shaft with a moulded head about 20 cm wide, carrying a fabric pad. A competent sweeper holds around 4 strokes a second under load. Everything in the story below is about that pad.

The brush that broke it#

The Hardline icePad arrived in the 2014–15 season. Its fabric behaved, in the description that stuck, "like sandpaper at a microscopic level": rather than polishing the pebble, it abraded it, and it did so directionally. Sweep across the front of a stone at an angle and the stone followed.

The technique that went with it was called directional sweeping, and the effect was dramatic enough that teams began sweeping with one player instead of two, because a single sweeper working the correct side of the stone did more than two working conventionally. Brad Gushue's rink demonstrated it at the Tour Challenge in September 2015 and the sport noticed.

Then Balance Plus responded with a fabric of its own — the "Blackhead", also called Black Magic — which was more powerful still.

2014season the icePad first won with
22teams who banned the fabrics themselves
50+brush variants tested at the summit
1fabric legal afterwards

The season, month by month#

The 2015–16 season is the whole story. It took about seven months from the first serious complaint to a permanent rule.

2013–14 A former curler, John Cullen, tries a new brush-head fabric and passes the recommendation to Mike McEwen's Manitoba rink — the origin point of the whole affair.
2014–15 McEwen's team uses the Hardline icePad and has an outstanding season: the Canada Cup, two Grand Slams, five tour events, and first place on the World Curling Tour Order of Merit. Reid Carruthers' team adopts the heads too. Nothing is against the rules.
Sept 2015 At the Tour Challenge, Brad Gushue's rink demonstrates directional sweeping publicly — including sweeping with one player rather than two.
Oct 2015 The flashpoint. At the Stu Sells Toronto Tankard, Balance Plus's competing fabric meets Hardline's head to head: Glenn Howard against Mike McEwen. The game runs over three and a half hours — more than an hour long — because McEwen's team has to clean the ice after every Howard shot to remove the damage the other brush is doing to it.
Nov 2015 Twenty-two of the top men's and women's teams on the World Curling Tour sign an agreement not to use the new fabrics. The tour formally asks players to stop. Days later, World Curling imposes a moratorium banning modified, custom-made and home-made brush heads, first at the Pacific-Asia Championships and then at the European Championships. Uppsala University confirms the icePad inserts are scratching the ice.
Winter 2016 An improvised season. Hair brooms are banned for front-end players at the Scotties and the Brier; broom-swapping between shots becomes a legitimate tactic; a provincial final turns on whether a particular brush counts as "commercially available" after it sold out. Kevin Koe's Alberta rink masters the chaos and wins the Brier, then the world championship.
May 2016 The Sweeping Summit at Kemptville, Ontario. Athletes, ice technicians and scientists from Canada's National Research Council test more than fifty brush heads and sweeping techniques using robots and GPS tracking.
Sept 2016 One approved fabric, for everyone, in every sanctioned event. Curling Canada follows. The affair is over in eleven months.

The part where the players fixed it#

The detail worth dwelling on is that the sport was rescued by the people with the most to lose by rescuing it.

In November 2015, twenty-two of the strongest teams in the world — including teams whose sponsorship arrangements were with the manufacturers involved, and teams that had won a great deal of money using the new heads — signed an agreement to stop. No rule required it. No governing body had yet acted. They did it because the games had stopped being curling.

A true curler never attempts to distract opponents, nor to prevent them from playing their best, and would prefer to lose rather than to win unfairly.
The Spirit of Curling, opening page of the rulebook

That passage is not decoration. It is printed on page two of the rules, before any rule, and Broomgate is the clearest case on record of it doing actual work. More on what it means in practice on etiquette and the spirit of curling.

The Sweeping Summit#

The Kemptville summit in May 2016 is the other thing curling got right, and it is a model of how to settle an equipment dispute in a sport whose physics is contested.

Rather than argue from principles nobody could agree on, they measured. Athletes, ice technicians and National Research Council scientists put more than fifty brush variants through controlled tests, using delivery robots for repeatability and GPS tracking for the trajectories. The question was not "which theory of curling is right" — that was and is unresolved — but "how much does this specific pad move this specific stone".

The answer was: too much, for several of them. The regime that followed is frankly prescriptive, and deliberately so.

The rules that came out of it#

Two layers. The rulebook governs the action; a separate equipment specification governs the object.

What you may do with a brush#

Rule R8 of the Rules of Curling now reads, in part: sweeping can be in any direction and need not cover the whole width of the stone, but the brush head must not be raised in front of a moving stone, must not deposit debris in front of it, and each stroke must finish to one side or the other. In officiated play, umpires watch for it: a first violation is a warning to the whole team, and any later violation in the same event costs the stone.

What a brush may be#

Only World Curling-approved heads may be used in elite competition, and approval is of the complete head — fabric, foam, backing, all of it together — rather than of a fabric that anyone may then mount on anything. Custom, modified and home-made heads are out. There is a published approved-product list, and it changes.

And then it happened again#

It would be neater to stop in 2016. The sport did not.

Through the 2024–25 season complaints returned, this time about foam. The approved fabric was being stretched over harder foam inserts, and the resulting heads were reported to be over-effective — the same problem in a different layer of the sandwich. In January 2025, elite curlers from fifteen men's and fifteen women's teams submitted a Proposal for Fair Play in Curling to World Curling, and some teams again agreed among themselves not to use the equipment in question.

World Curling revised the specification for the 2025–26 Olympic season: compression modulus was dropped as a measure in favour of compression at 779 N, and foam must now carry marks identifying its year of manufacture. The changes apply to component-style heads — covers and sleeves over moulded foam — while traditional heads with fabric stapled directly to the head remain approved.

The structural problem

Curling cannot write a rule that says "a brush may not steer the stone", because nobody can calculate from first principles how much a given brush steers a stone. So the rules have to specify the object instead — this foam, this fabric, this compression at this force — and every specification of an object is a specification somebody can engineer up to the edge of. This will recur until the physics is settled, which is one more reason the physics is worth settling.

Sources#

BroomgateThe most complete public timeline of the 2015–16 season, and the source for the specific events and dates above.
Curling’s only scandal: how Broomgate changed the game forever CBC SportsRetrospective interviews with the people involved.
Primary Specifications for brushes in elite curling World CurlingThe current equipment regime and the approved product list.
Primary Sweeping equipment regulations update for the 2025–2026 season World Curling, 2025The foam revision: the compression measure at 779 N, and the year-of-manufacture marking requirement.
Primary The Rules of Curling, R8: Sweeping World Curling, 2025What may and may not be done with a brush, and the penalties.

Elsewhere#

Five years after curling’s biggest scandalThe trade press looking back, with more of the manufacturer politics than the mainstream coverage carried.
The mechanism that puts the curl in the curling stone revealedUppsala University, whose scratch-guide work is both the best-known theory of curl and the group that confirmed the icePad was scratching the ice.

What sweeping does, with the numbers Choosing a brush of your own