Fishing vessels must keep their holds chilled in order to safely store caught stock. In addition to ice and refrigeration equipment, the hold’s insulation is key for maintaining the proper temperatures and reducing energy costs. There are multiple types of insulation available, each with benefits and disadvantages. Understanding the properties of these materials, and taking them into consideration along with factors such as the size of the craft and the structure of the hold, will allow industrial fishermen to choose the optimal insulation for their fishing vessels.

Polyurethane Foam

Polyurethane foam is one of the top options for insulating materials. A man-made polymer, the foam is filled with various inert gases to slow heat conduction. It’s lightweight and moisture-resistant, and has multiple methods of installation, allowing for flexible construction. Boards or slabs of pre-made foam can be cut and placed along walls. Polyurethane can also be mixed as a liquid and poured into place or injected into cavities to form a solid mass, or else sprayed in layers, adhering to most woods and metals as well as itself, a useful property for insulating ship holds.

One main disadvantage of polyurethane is its water permeability compared to some other materials. While moisture won’t damage it, the foam becomes heavy and its insulating properties are reduced when waterlogged. Fiberglass-reinforced plastic linings are used to block moisture, but are more expensive. Polyurethane also can burn when exposed to fire, and though it’s usually treated with flame retardants it can produce toxic chemicals when burning. It’s also pricier than other insulation options, and not available in all markets.

Polystyrene Sheets

Another artificial polymer, extruded polystyrene is better known as Styrofoam. When molded into sheets of various sizes and widths, it can provide significant insulation that is not as permeable to water as polyurethane. However, like polyurethane it is flammable. Polystyrene also starts to break down in direct sunlight, and can react with certain solvents, making it impractical for any hold that has a fiberglass lining directly applied over the insulation.

Cork Board

Made of natural cork wood, cork boards were once among the most popular insulating materials on the market. Nowadays, however, a shortage of cork trees means the board is expensive compared to other options, and generally has limited applications. While it’s more burn-resistant than most woods, it can’t be used in temperatures over 65 degrees Celsius, and its high rate of absorbing water vapor makes it impractical for widespread use on ships and boats.


Matting composed of fiberglass is resistant both to fire and heat as well as chemicals, and is a good thermal insulator. It’s still water-permeable, however, losing effectiveness when damp, and offers little in the way of structural support to a hold. Though it’s generally inexpensive and comes in a variety of thicknesses for ease of installation, if it’s incorrectly arranged it can settle in place, leaving gaps in the insulation.

Wood Shavings, Sawdust and Straw

Organic materials such as straw, wood shavings and sawdust have a long history of being used as insulators. Whether packed or poured as loose fill into spaces or used to block gaps, the relatively light densities of the materials and the air trapped between them forms a useful thermal barrier, if not as effective at blocking heat by volume as man-made materials such as polyurethane and polystyrene. Straw and sawdust are also extremely cheap and easy to come by almost anywhere.

However, they have several major drawbacks. Wood particles and straw are flammable when dry. They also are likely to shift and pack down when subjected to engine vibration, leaving inefficient spaces where the cold can be lost. These materials are also very prone to absorbing water and moisture. Not only does dampness increase their weight and lower their insulation efficiency, but they can start to rot and are more likely to develop mold and mildew than artificial materials. Insects and other pests may also make nests in sawdust or straw.

Sealed Air Space

Since the insulating properties of most insulation actually is provided by the air or other inert gases trapped in the foam or fibers, it’s no surprise that plain air can also act as an insulator. Gases conduct heat less than liquids or solids, since the molecules which transfer thermal energy are more dispersed in the gaseous state. Air is as lightweight as it’s possible to be, and of course free. However, to effectively employ air as an insulator, it must be held in completely sealed compartments, or else circulating drafts of heat can counter-productively raise the hold’s temperature, rather than keeping it low. Air also provides no structural support and requires substantial empty volume, so may not be a practical choice for some vessels.

Whatever type of insulation is installed in the hold, Semco’s industrial cooling systems can provide the right level of refrigeration. Every system is rigorously designed and customizable to the exact specs for each client, ensuring that fish are cooled efficiently and effectively chilled.