Peak breakaway force is the highest tension, in newtons, recorded while an unloaded shoe is pulled horizontally across the first 20 mm of travel. The shoe is pulled from the heel by an inextensible cable; the reading is taken on the dynamometer's peak-hold function.

The 20 mm window matters. With a polymer outsole the contact conforms over the first few millimetres, so the force sometimes keeps climbing briefly after the shoe first moves. On wet surfaces this is more pronounced: force tends to rise through the travel rather than peak at breakaway, consistent with water being progressively squeegeed out of the contact area, adding a suction-like component as the sole advances. We report the peak over a fixed 20 mm window for every model, measured the same way, rather than the instant of first movement.

This is not a coefficient of friction, not a slip-resistance rating, and not a safety rating. It is a comparative bench measurement of one property, under one set of conditions.

Smooth Galvanized Steel Sheet, 0.4 mm. Plain galvanized sheet, 0.4 mm nominal thickness, bonded flat to a rigid backing board so it cannot deform or lift under load. An unprofiled galvanized steel sheet was used to provide a uniform steel contact surface independent of roofing profile geometry — several roof profiles include smooth, flat areas of their own, standing seams among them, so this surface also stands in for those sections.

Painted R-Panel, 29 gauge. Pro-Rib steel panel, painted finish, 29 gauge after coating. The shoe is positioned on the flat pan between ribs, in the same position for every pull.

Dry. Surface and outsole wiped clean and dry. Ambient temperature logged for every pull.

Wet. A sponge saturated with clean water is drawn across both the test surface and the outsole immediately before the pull, until both are visibly saturated. No surfactant. Both are re-wetted before every individual pull.

Both Navail models lead every competitor pair in every condition tested, but the two don't lead by the same margin everywhere. MagSteel Flow reaches its highest readings of the whole campaign on flat smooth steel, while MagSteel edges ahead on the ribbed R-Panel profile, dry and wet alike. Both perform strongly across every surface tested; each simply excels most on a different one.

The three competitor models cluster well below both Navail models in every cell, and the gap widens on wet surfaces.

• The shoe is unloaded. Normal force here comes from magnetic attraction plus the mass of the shoe. In use, a worker's body weight is also on the sole.
• Six pulls per cell. Enough to show a difference of this size with the dispersion observed, not enough to separate models that land close together.
• Sizes are not standardised across models — see the samples table.
• New samples and new surfaces only. No wear, no scuffing, no weathering.
• Two surfaces. Corrugated, aluminium and non-magnetic surfaces are not covered yet.