The most common types of outsoles used for safety footwear are:
PU MONO (SINGLE) DENSITY
It is a material with a substantial weight and a good comfort reaction. It has a good resistance to few chemical agents and oils, but no resistance to the strong acids. The resistance to temperatures goes from -10/-20 to +130 max 140 degrees . The softness gives a good grip to this material giving it a slip resistance similar to TPU and rubber.
Recommended usage: Indoor and not very aggressive work places.
PU/PU
It is a double-density profile sole made of PU. It has a good resistance to few chemical agents and oils, but no resistance to the strong acids. The resistance to temperatures goes from -10/20 to 120 max 150 degrees. The dual density PU midsole provides good impact absorption and wearing lightweight comfort.
Recommended usage: Indoor and outdoor, not really suggested for contacts with chemical agents, acids & water.
PU/TPU
It is particularly sturdy, abrasion-resistant and flexible. TPU provides higher performances: abrasion resistance, slip resistance at a very good level and also similar to single density PU and rubber, flexibility. On the average usage, it is more durable than PU and it has an higher resistance to low temperature from -5 up to -20 degrees. Not very resistant to high temperatures: maximum 100 degrees.
Recommended usage: Indoor and outdoor, cold weather, not really suggested for contacts with hot surfaces.
MONO DENSITY RUBBER
Exceptionally sturdy: temperature-resistant from -30 up to 300°C, hard to penetrate for sharp objects and resistant to fuels, oils, microbes and numerous chemicals. However, rubber is much heavier than PU and TPU, and is less flexible when subjected to cold temperatures. The rubber outsoles are also known for the great slip resistance similar as single density PU and TPU. RECOMMENDED USAGE: indoor and outdoor, in contact with oils, chemicals, acids. If HRO certified, it is also recommended for contacts with hot surfaces. It is a compact and heavy material hence it is not the best choice against foot fatigue.
Recommended usage: Indoor and outdoor, cold weather, not really suggested for contacts with hot surfaces.
The common types of outsoles constructions methods / bonding used for safety footwear are:
Goodyear Welt
Using an insole with a wall or rib that is positioned closed to the edge of the insole. During lasting, the upper is secured to this wall. Sole is then positioned with adhesive to the shoe outsole and is stitched through the welt base. This is the most traditional & labour intensive with the highest price point to the end users.
Recommended usage: Typically wet & higher temperature environments, volatile environments. Such as Oil & Gas, Offshore, Oil Drilling. Etc.
Cemented Bonding
In this process the upper and the sole are glued together. In this case the sole is fabricated first, with a separate machine. Once a boot’s upper is shaped and completed, the sole is attached with an adhesive. This is the fastest method with least production time.
Recommended usage: Environments with flat surfaces, such as assembly lines, manufacturing jobs, warehouses, and roofing and service applications, as well as jobs where the majority of time is spent standing or kneeling.
Injection Molding
Injection of polyurethane, in which the sole of polyurethane is created and directly attached to the upper. The upper is placed into a mold (normally made of aluminum or Teflon), then polyurethane is injected into the mold, and when it cools it becomes solid and sticks to the upper. This process fixes together the upper and the sole very firmly.
Recommended usage: Various types of working environments for the masses. Such as Constructions, Engineering, Logistics, F&B, Service Line, Shipping, Shipbuilding, as well as jobs where the staff are numerous.
Understanding Footwear Markings
Safety EN 20345 Standards |
Class | Basic Toe Protection (200Joule) |
Slip Resistant (SRA/SRB/SRC) |
Closed Heel | Antistatic | Oil & Fuel Resistant |
Water Repellent | Mid-Sole Puncture Resistant | Cleated Outsole |
---|---|---|---|---|---|---|---|---|---|
S1-P | I | × | × | × | × | × | |||
S2 | I | × | × | × | × | × | |||
S3 | I | × | × | × | × | × | × | × | |
S4 | II | × | × | × | × | × | × | ||
S5 | II | × | × | × | × | × | × | × | × |
- SRA: Work shoes with SRA certification provide slip resistance on a ceramic tile floor with lauryl sulphate.
- SRB: Safety shoes with SRB certification provide slip resistance on a steel surface with glycerol.
- SRC: Work shoes with SRC certification combine the slip resistance of SRA and SRB. This safety footwear therefore offers the highest slip resistance.
- HRO: Resistance to hot contact of the outsole (test at 300ºC). When tested rubber and polymeric outsoles should not melt or crack when bent.
- WR: Water resistance (for S2 and S3 only). The total wetted area inside the footwear shall be ≤ 3cm² when tested.