In practice, simply increasing the number of layers past a certain value will not improve performance. As the no. of layers increases, radiative heat transfer becomes small compared with conductive “shorts” between layers and other losses. Taking all these factors into account, about 25 layers usually suffice to obtain a minimum overall conductance value.

==== Working of MLI ====

Lets understand this with an example.

Imagine a square meter of a surface in outer space, at 400 K, with an emissivity of 1, facing away from the sun or other heat sources. From the Stefan–Boltzmann law, this surface will radiate 1452 watts. Now imagine placing a thin (but opaque) layer 1 cm away from the plate, thermally insulated from it, and also with an emissivity of 1. This new layer will cool until it is radiating 726 watts from each side, at which point everything is in balance. The new layer receives 1452 watts from the original plate. 726 watts is radiated back to the original plate, and 726 watts to space. The original surface still radiates 1452 watts, but gets 726 back from the new layers, for a net loss of 726 watts. So overall, the radiation losses have been reduced by half by adding the additional layer. <br \>

MLI is composed of multiple layers of low-emittance films. <br \>

The simplest MLI construction is a layered blanket assembled from thin embossed Mylar sheets, each with a vacuum-deposited aluminum finish on one side. As a result of the embossing, the sheets touch at only a few points, and conductive heat paths between layers are thus minimized. The layers are aluminized on one side only so that the Mylar can act somewhat as a low-conductivity spacer. Higher-performance construction is composed of Mylar film metalized (with aluminum or gold) on both surfaces with silk or Dacron net as the low-conductance spacers. <br \>

Heat transfer through MLI is a combination of radiation, solid conduction, and, under atmospheric conditions, gaseous conduction. These forms of heat transfer are minimized in different ways. Radiative heat transfer is minimized by interposing as many enclosing reflective surfaces (metalized sheets) as is practical between the object being insulated and its surroundings. Solid-conduction heat transfer is minimized by keeping the density of the low-conductance spacers between the reflective surfaces as low as possible and making the blanket "fluffy" to minimize contact between layers. <br \>