Materials used for sea kayaks

PE and fiberglass are by far the most common materials used for kayak manufacturing. 95% of all plastic kayaks are made of Polyethylene (PE). PE is the plastic best suited for roto moulding which is the method used to make sea kayaks. PE comes in many variations. The most common used in kayak manufacturing are:

• LLDPE (Linear Low Density Polyethylene)
• MDPE (Medium Density Polyethylene)
• HDPE (High density Polyethylene)

LLDPE is strong, smooth and stretches easily. It is used for White Water kayaks where there is a high risk of hitting stones and cliffs at high speed.

HDPE is lighter and stiffer. The disadvantage of HDPE is a more friable plastic. If a HDPE kayak hits a stone or cliff at high speed it can cause a crack in the kayak hull. The brittleness of a HDPE kayak increases at low temperatures.

MDPE is used by many manufacturers as a name for their own specialized plastic composition. MDPE variations are a matter of many years of experience and research, by leading plastics manufacturers to achieve the right ratio between rigidity, durability and resilience. At DesignKayaks we use a special mixture of MDPE called XDPE with the best properties from both types of plastic.

Talking about PE kayaks the conversation often turns to structure rather than the actual material. PE Kayaks comes in 1, 2 and 3 layer plastic:

• 1 layer PE gives you the most sturdy structure, but the least stiff. These characteristics make 1-layer well-suited for white water kayaks. Due to the length of a sea kayak 1-layer sea kayaks often get really heavy because of the need of much material to create the stiffness.
• 2-layer has a PE layer on the outside and a foam layer on the inside. The foam layer provides a lightweight and yet stronger structure compared to 1-layer. 2-layer is only used for sit-on top kayaks and surfski where you never touch the inside of the kayak.
• 3-layer kayaks have a lightweight foam layer sandwiched between an outside layer providing resistance and protection and a smooth thin inner layer. This structure provides a much stiffer and yet low weight compared to 1-layer kayaks.

Multilayer structures are the most complicated to manufacture. In the following we take a closer look at the 3-layer structure. This structure is commonly used for sea kayaks, but it comes in very different qualities.

Rotomoulding is the method for making PE kayaks. Here the mould is fitted and made ready for the rotation proces in the oven.

The illustration shows: A) The outside layer of the hull. B) The middle foam layer. C) The inside layer of the hull. D) The combined 3-layer structure

If the foam layer does not reach the right temperature it will not expand to the desired level. Over time this will cause irregularities in the surface of the kayak. Too high temperatures cause the foam to collapse resulting in deform kayaks.

Poorly manufactured 3-layer kayaks do not achieve the desired stiffness and will soon get irregularities at the bottom part of the hull. To avoid this some manufacturers add extra plastic to the out-layers the outcome of this is an extremely heavy kayak.

Poor quality of a 3-layer kayak can be hard to spot on a new kayak. If you consider buying a 3-layer kayak keep an eye on the following to avoid poor quality:

1. Stiffness: Try to press on both sides of the kayak at bow or stern. It should not be flexible, but stiff and still not too heavy. Compared to a similar 1-layer kayak the 3-layer must be stiffer and lighter.

2. Price: Beware of deals that look too good to be true. It takes more work processes to produce 3-layer kayaks and materials are more expensive.

3. Brand: Is it a well-known brand or can you find the manufacturer behind the brand? In that case you can feel pretty confident that the quality of the kayak is ok.

Want to know more about the production of DesignKayaks? All sea kayaks from DesignKayaks are manufactured at our factory DSK Mothership in George South Africa. Read more about our factory.

What material is right for you? Well, It all depends on how much money you want to spend and how you want to use your kayak. Here are a few pointers:

Durability: 1-layer kayaks are very durable. That is why white water kayaks are typically made in 1-layer. A 1-layer kayak is about 4,5-5 mm making it almost impossible to break.

The outer layer on a 3-layer kayak is much thinner and you should avoid dragging it on concrete and asphalt. However you should not worry about the durability of a 3-layer kayak. PE is a very strong material. Paddling on ocean and lakes is nothing at all to worry about – even with landings on rocks.

Composite is by far the most fragile material that requires you to be more careful in how you handle your kayak.

Price: 1-layer is the simplest and fastest way to produce kayaks keeping the price down, but you will get a lot more quality by paying a little more for a 3-layer kayak. Composite is the most expensive material because production is very labor intensive.

Stiffness and weight: 3-layer offers you a lot extra on both stiffness and weight. It is faster than 1 layer and lighter at the same time. If you want extra stiffness and the lowest possible weight composite is the ultimate choice.

Repair: 1-layer is very easy to repair and you can do it yourself. If your composite kayak needs repair you will need a professional, but even larger damage to the boat can be fixed. 3-layer is the hardest to repair because the layers react differently to heat, however smaller leaks are simple to fix.

Environment: One thing is what is right for you, but what is better for the environment? There is a lot of debate about plastic and for good reasons, but plastic is much better than composite. The plastic used for kayaks can be recycled whereas most composite is waist deposit.

Just to sum it up. There are a lot of stuff to consider! But try to be honest in your assessment of what you need. To really appreciate a composite kayak you need to paddle a lot and at the same time be more careful because of the fragility of the material. A 3-layer PE material will get you a long way in terms of stiffness, durability and value for money.

Choose 1-layer PE if:

If price and durability are the most important for you and you do not mind a heavy kayak.

Choose 3-layer PE if:

If you want a fast and light plastic kayak with good durability you get really good value for money.

Choose composite if:

You want a lighter kayak with maximum stiffness and dont worry to much about price.

You can read our guide to composite materials here.