For routine low-stress applications, tin protects copper contact surfaces with a low contact-resistance coating that is perfectly adequate for temperatures up to circa 60degC. It should not normally be used in thick layers and must not be exposed to service temperatures above circa 80degC. Diffusion of tin becomes rapid above about 100degC and seriously damages the conductivity of copper; tin-coated finely- stranded cables can easily become dangerously resistive if allowed to overheat. Tin is also unsuitable for environments below circa -20degC where it forms an amorphous allotrope that can detach as a powder. Standard terminals are normally supplied with a 5µ tin coating and are intended for use at controlled working temperatures. Tin coatings are solder-compatible but the high temperatures of the soldering process can cause localised increases in copper substrate resistance, particularly in fine-stranded cables.