Steam locomotive
Boiler insulation

The term for pipe and boiler insulation is "lagging" which derives from the cooper's term for a wooden barrel stave. Two of the earliest steam locomotives used wooden lagging to insulate their boilers: the Salamanca, the first commercially successful steam locomotive, built in 1812, and the Locomotion No. 1, the first steam locomotive to carry passengers on a public rail line. Large amounts of heat are wasted if a boiler is not insulated. Early locomotives used lags, shaped wooden staves, fitted lengthways along the boiler barrel, and held in place by hoops, metal bands, the terms and methods are from cooperage.

Improved insulating methods included applying a thick paste containing a porous mineral such as kieselgur, or attaching shaped blocks of insulating compound such as magnesia blocks. In the latter days of steam, "mattresses" of stitched asbestos cloth stuffed with asbestos fibre were fixed to the boiler, on separators so as not quite to touch the boiler. However, asbestos is currently banned in most countries for health reasons. The most common modern-day material is glass wool, or wrappings of aluminium foil.

The lagging is protected by a close-fitted sheet-metal casing known as boiler clothing or cleading.

Effective lagging is particularly important for fireless locomotives; however, in recent times under the influence of L.D. Porta, "exaggerated" insulation has been practised for all types of locomotive on all surfaces liable to dissipate heat, such as cylinder ends and facings between the cylinders and the mainframes. This considerably reduces engine warmup time with a marked increase in overall efficiency.
detectable_content:postscript, length_constraints:number_paragraphs[2], language:response_language[German]