A wide range of methods and materials are available to insulate the fish holds of Bristol Bay gillnetters, and when installed properly, insulation will provide an adequate thermal barrier for use with slush ice or RSW, and last for decades. With the cost of insulating a Bristol Bay gillnetter’s fish holds falling in the $8,000-$12,000 range the investment can easily be paid off in a single season and provide decades of additional income potential.

If you’re serious about delivering a quality product and maximizing the value of your catch, insulating your fish holds is the perfect place to start.

There are many methods and materials used to insulate the fish holds of Bristol Bay gillnetters, described below are a few of the more common. As long as the insulation job is done properly and maintained, all of these methods should perform well and last for decades.  

Spray Foam Insulation

A spray foam insulation job, when finished with a durable exterior coating such as fiberglass or epoxy, is a relatively quick and inexpensive option for aluminum or fiberglass boats, and provides a more than adequate thermal barrier.

One advantage of this method is that the foam easily fills small voids and contours, making it a good option for boats with hold configurations that have many angles or overhangs. A spray foam job will require little effort or expertise on the behalf of a boat owner or professional and can be completed in as little as a few days.

As with most insulation jobs, it is important to ensure moisture does not accumulate between the foam and the hold walls and floor to prevent a potentially costly corrosion issue. Half this battle lies in good adhesion of the foam to the hold surfaces. Properly preparing and cleaning the fish holds before the foam is applied is essential to closely follow the instructions for the product being used. Additionally, it is a good idea to check the fish hold surfaces for cracks or other damage that might allow water to seep into the foam before and after each season.

Find a DIY Guide to Spray Foam Insulation here.


  • High return on Investment—Insulating your fish holds is the best investment you can make in your boat.
  • Quickest way to insulate your fish holdsIncluding hold prep time, a spray foam insulation job can be done in as little as a few days, making it a very convenient option.
  • Relatively inexpensive—The cost of a spray foam job falls in the $8,000-$12,000 range for most boats, making it an affordable option for most fishermen.
  • High r value—Spray foam is a very effective form of insulation and a thicker layer can easily be applied to warmer areas like the engine room bulkhead when needed.
  • Can be applied to virtually any hold configuration—Spray foam easily fills small voids and contours making it a great option for boats with unconventional hold configurations that would make cutting and fitting stiff insulation sheets difficult.


  • Potential for corrosion issues—If water seeps between the foam and aluminum corrosion can cause unseen damage, leading to costly repairs.

Nida-Core Insulation

Nida-Core is a honeycomb structured PVC core material that typically comes in 4’ x 8’ sheets and is available in a range of thicknesses. It is lightweight, does not absorb water and has good insulating properties because of the air voids within each honeycomb cell. These attributes have made it a popular choice for flush decks and fish hold replacement jobs, and more recently as a supplemental layer of fish hold insulation for fiberglass and aluminum boats.

As a lightweight core material with no real strength of its own, Nida-Core must be laminated with a layer of fiberglass for any fish hold application, and purchasing pre-laminated sheets from suppliers is well worth the added cost. For a typical hold insulation job, where the existing hold structure is not being replaced, spacer strips of Nida-Core are spaced evenly and adhered to the hold surfaces to provide an air gap, then half-inch thick sheets laminated on one side are cut to fit, adhered to these spacers and tabbed together with fiberglass along their adjoining seams. The air gap created by the spacers provides additional insulation and helps mitigate corrosion issues that could result from moisture buildup.

With this type of insulation method it is important to install a drain or access plug in the bottom of each hold so any water that does accumulate can be drained periodically. Insulating your holds with Nida-Core can save you thousands of dollars over a professional spray foam job if you do most of the work yourself but is best suited for boats with simple hold configurations, to keep the labor of fitting, cutting and fiberglass tabbing within a practical realm.


  • High return on Investment—Insulating your fish holds is the best investment you can make in your boat.
  • Least expensive way to insulateIf the boat owner does most of the labor, a Nida-Core insulation job can cost as little as $4,000 making it a very affordable option.
  • Little risk of corrosion—As long as the air void at the bottom of each hold can be checked and drained if necessary, the gap between the insulation and the hold surfaces will prevent corrosion from occurring.
  • High r value—If done properly this insulation method will provide an r value very close to that of spray foam for about half the price.


  • Labor intensive—For a Nida-Core insulation job to be more economical than spray foam most of the labor must be performed by the boat owner.
  • Not practical for all hold configurations—Fish hold configurations that have extreme contours or require many smaller pieces of Nida-Core to be cut, fitted and tabbed together could increase the amount of labor required beyond practicality, making spray foam a better choice.

Double-Walled Insulation

Many new aluminum gillnetters are being constructed with double-walled fish holds, and for good reason. The air gap between the relatively warm hull and the fish hold surface not only provides adequate insulation for an RSW application, it is maintenance free and – as long as these voids are watertight or periodically drained – the risk of corrosion is low. The drawbacks of this insulation method are that it’s expensive and generally doesn’t perform as well as spray foam or Nida-Core. Furthermore, in aluminum vessels, double-walled insulation alone does not isolate your fish holds from other heat sources on your boat, your engine room or the compressor on your RSW unit. Remember, aluminum is a conductor, it will transfer heat from any source in contact of your boat.


  • High return on Investment—Insulating your fish holds is the best investment you can make in your boat.
  • Low maintenance—As long as the welds are in good shape, double walled aluminum insulation requires no maintenance and is easy to clean. Plumbing the holds for RSW is also easier than with many other insulation methods and is more durable and less prone to water seepage.
  • Little risk of corrosion—Because there is no foam to trap moisture against the aluminum, the potential for corrosion issues are low.
  • Performs well with RSW systems—This insulation method provides an adequate thermal barrier for use with an RSW system if fish holds are properly isolated from major heat sources.


  • Expensive—Aluminum is not cheap and neither is welding, making this one of the more expensive ways to insulate your holds.
  • Not very effective for use with slush ice—in most situations where slush ice is the primary means of chilling one’s catch, the higher r value of Nida-Core or spray foam are more effective options.