What type of materials are often included in thermal system insulation?

The correct choice refers to materials commonly found in thermal system insulation, specifically fiberglass or mineral wool insulation. These materials are designed to minimize heat transfer, thereby maintaining desired temperatures within systems such as pipes, ducts, and boilers. Fiberglass insulation is widely used due to its effectiveness in thermal resistance and its lightweight nature. Mineral wool, also known as rock wool, provides similar thermal properties and is often favored for its fire-resistant characteristics.

The other suggested materials do not primarily serve as thermal insulation. Soundproofing panels, for example, may reduce noise but do not provide the specific thermal resistance needed for system insulation. Fire-resistant materials can play a role in protecting structures from heat but are not necessarily designed for thermal insulation purposes. Water-resistant membranes, while useful in preventing moisture penetration, do not contribute to thermal resistance and are more focused on protecting against water damage rather than controlling heat transfer.

Overall, fiberglass and mineral wool are essential for ensuring efficient thermal insulation, making them the appropriate answer in this context.