Proper Materials for Boats

Hi everyone,

I am writing to ask you about what materials would you recommend using in a boat.

My idea is to give shape to the hull with foam and then coat it with fiberglass.

The foam will be molded using a cutting numerical control machine (CNC) and I am considering two core materials:
- Expanded Polystyrene (EPS)

- Extruded Polystyrene (XPS)

Which one would you recommend me to use and why?

Thanks for your time.


Esteban Caligaris

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  • Esteban, check out this post. This is the best example of balsa panked construction, the end structure is then covered with a light glass layer with polyester resin.
    Again without knowing your boat design I can only recommend this as a consideration.

    • Thanks for your reply Richard!

      I'll give it a look and a try.


      Esteban Caligaris

    • Estaban,  The post Richard is referring to is mine.  The balsa was covered with 6 oz. glass cloth with epoxy resin.  I used West System epoxy.  It is extremely strong and each 44" x 8.5" hull weighed in at under a pound IIRC.


      David R. Boulanger

  • Hi Esteban,

    My answer would be neither!

    Reason: when you say fiberglass I am assuming you mean Polyester resin and glass fibre (normally chop strand matt)?

    Neither material is good for a core material. In a structural sense the cellular bond strength is weaker than the inner and outer skins. The main reason one uses a core is to separate the inner and outer skins to create an I-beam effect. Two surfaces held in parallel. The greater the distance between the two plains/surfaces the greater the flexual strength. With a weak core material like polystyrene the two surfaces will not stay in parallel under load.

    Of course this is variable depending on the size of the boat.

    If you are intending to use Polyester resin then this will not work. Polyester contains styrene! This will melt the polystyrene upon contact.

    Without knowing the size of the boat you plan to construct I can suggest two options:

    1. You can use a alternative core material PVC foam (surfboard foam) or balsa wood. Easy to shape, great with a CNC.
    2. Build your boat monolithic. Use the Polystyrene as a male or female mould, cover it with packing tape to protect the polystyrene and mould a piece. The draw back for this method is the time you will spend finishing the hull surface due to the uneven surface of the packing tape.
    3. Use and epoxy resin system. Still not recommended. It is not recommended to use chop strand matt with epoxy as the matt uses styrene as a binder with inhibits the cellular formation of the epoxy cell structure, ending with a weak product.

    If you want to tell me about your boat I can better advise on material and construction methodologies? either post here or email me: (website:


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