The outer jacket

The inner insulation — mineral wool, PUR, PIR, elastomeric foam or another type of pipe section or mat — is only one part of the installation. It provides the thermal resistance, but it cannot stand alone. A layer of mineral wool is soft, fibrous and moisture-sensitive, and with nothing on the outside it falls apart. The outer cladding is the outermost, protective layer, and it has five tasks that all have to be met at the same time:

1. Hold the insulation in place. It presses pipe sections, lamella mats and wired mats in against the pipe so they do not slip, fall down or open up at the joints. The outer cladding is therefore — together with lacing, banding and tape — part of the retention [Saint-Gobain Isover, Retention of ISOVER Insulation, May 2020].
2. Protect against moisture. Rain, splash water, condensation, cleaning water and humidity cause the insulation to clump, lose its λ-value and rot. The cladding is the first barrier — and at the same time the one that has to be tight enough that water does not penetrate, yet open enough that any diffused moisture can escape (or completely vapour-tight on cold pipes, where moisture must be kept out).
3. Protect against mechanical wear. In technical rooms, pipes get knocked by wheelbarrows, ladders and forklift trucks; outdoors the installation is attacked by birds, hail and vandalism. A soft felt-and-canvas surface is scratched open by a fingernail; a 0.9 mm alu sheet can withstand being struck by a wheelbarrow.
4. Protect against UV radiation. Outdoors, sunlight destroys cotton canvas (it changes colour and crumbles), PVC jacketing (it becomes brittle and cracks) and ordinary elastomeric foam (it develops cracks and shrinks) within a few years. Aluminium and stainless steel, by contrast, are UV-stable for decades.
5. Provide a surface for hygiene, aesthetics or energy radiation.
   • Hygiene: In hospitals, laboratories and food production, the cladding must be able to be wiped down with disinfectant. A smooth PVC jacketing or a brushed stainless sheet-metal cladding is the right choice.
   • Aesthetics: In visible installations (lobbies, shops) the cladding determines the impression — painted felt+canvas looks classic, bright alu looks industrial, white PVC is neutrally technical.
   • Energy: A bright metal surface radiates only 5-13 % of the heat that a black-painted or matt surface radiates. This means the radiation loss from the outermost surface is reduced dramatically — and in practice it allows a thinner insulation at the same DS 452 class [Isover HVAC Handbook, 9th ed., Dec. 2022, pp. 6-7].

The last point is easy to overlook: the outer cladding is not just protection — it actively figures in the energy balance.

In Danish technical insulation there are four basic choices for the outer cladding. Each of them has its own product-range page with detailed material data, standards and installation guides:

1. Felt and canvas — the classic, flexible finish

Three layers: felt innermost (hides the substrate), canvas on top (the woven, flexible exterior), and paste that stiffens the whole thing into a hard shell. It is a craft tradition from the 1900s that is still part of the curriculum on the AMU course 49058 and is still found in older basements, boiler rooms and institutions. Cotton canvas + starch paste goes up to approx. 120 °C; glass or silica canvas + special paste handles high temperatures up to 500-1000 °C. The fire class is D-E for the standard variant, but glass canvas achieves A2.

[Detailed product-range page: /sortiment/pap-og-laerred]

2. PVC jacketing — the fast, smooth indoor standard

A thin, hard plastic film 0.30-0.50 mm thick that is rolled around the insulation and closed with PVC adhesive, pop rivets or tape. Manufacturers such as Danmat (ISOTOP), Armadan and Germany's Sebald (Isogenopak, Okapak) supply both roll material and thermoformed mouldings — bends, T-pieces, end caps and valve covers. Rigid PVC has a Vicat softening point of 76-81 °C; the practical operating limit is 60-65 °C on the film itself. The fire class is C_L-s2,d0 in a tested system with mineral wool. Not used outdoors without extra protection — PVC has no UV resistance [Bilcare TA S17 datasheet; EN 15701:2016].

[Detailed product-range page: /sortiment/pvc-folie]

3. Sheet-metal cladding — the robust, long-lasting choice

A thin metal sheet (0.5-1.0 mm) in aluminium (alloy 3003/3103/5052), alu-zinc, galvanised steel or stainless steel (AISI 304/316), folded around the insulation and joined with a snap-lock seam, pop rivets or self-tapping screws with a sealing washer. Fire class A1 non-combustible, service life 25-50 years outdoors as well as indoors, and bright alu gives an emissivity of 0.05-0.13 — i.e. low heat loss from the outermost surface. It requires prefabrication in a workshop from a production sheet and the industry agreement's "Standard for measurement and sheet-metal fabrication" [Association of Danish Insulation Companies; DS 419; DS 446; DIN 2605/3605].

[Detailed product-range page: /sortiment/pladekappe]

4. "Nothing" — elastomeric foam as its own cladding

Elastomeric foam (Armaflex and similar EPDM/NBR-based synthetics) constitutes a special case: the product is its own outer cladding. The closed-cell structure is itself vapour-retarding (µ ≈ 7,000-10,000), the smooth, black/grey outer surface can be wiped down, and it can handle operating temperatures from approx. -40 °C to +110 °C. On cold pipes indoors, elastomeric foam is chosen precisely because it replaces the insulation layer, the vapour barrier AND the outer cladding in a single product. The fire class is typically D-E (fire-retardant variants B_L-s3,d0). Outdoors and under UV exposure, however, an outer cladding (alu foil or sheet-metal cladding) is still required — elastomeric foam alone cracks in sunlight.

[Elastomeric foam has its own product-range page in planning — see provisionally /sortiment/cellegummi]

The most common mistake in choosing an outer cladding is to choose on price alone. A correct choice depends on context: indoors vs. outdoors, hot vs. cold, hygiene requirements, fire requirements and mechanical load. This matrix collects the typical choices:

The important principle: Sheet-metal cladding is the expensive, robust choice. PVC and felt+canvas are the cheap, indoor choices. Elastomeric foam is its own system. There is no single universal "best" choice — there are context-specific best choices.