Different Types of Plastic Used in Kayaks and Canoes
The following is a video of 10 year old HDPE Vs 6 month old LLDPE. The 6 month old LLDPE has worn straight through on the keel line (Note the repair) and was then rejected by the centre.
Below is a more comprehensive guide to plastics used to make kayaks:
There are three grades of plastics generally used to manufacture rotationally moulded kayaks.
High Density Linear Polyethylene HDPE:
Used in white water kayaks, sea kayaks and best quality angling kayaks. This grade of plastic has the best abrasion resistance, impact and splitting resistance, memory and UV stability.
A more difficult plastic to mould but the through life results are the best.
All these top end kayaks are a bit heavier (stronger). Strong plastics used in the moulding of sit on tops will in some cases show a slight ripple in the hull. This happens when the scupper drain holes contract and is more noticeable on kayaks that have stiff upper decks or standing platforms.
Sit in kayaks not having scupper drain holes are not affected. This is a fact of moulding life and does not affect the performance of the kayak.
The following is a statement from the director of Dagger & Wilderness Systems Kayaks:
Why Dagger & Wilderness Systems Kayaks Uses High Density Super- Linear® Polyethylene
As a kayak producer, choosing the correct material for manufacturing is one of the most important decisions you ever have to make.
Plastic is available in so many different forms but since most kayaks are rotomoulded, polyethylene has proved to be the most suitable material to use.
Unfortunately, many of the general purpose grades of polyethylene are not suitable for kayak use. They are categorised under LDPE (Low Density Polyethylene; 0.910 to 0.925 g/cm3) and LLDPE (Linear Low Density Polyethylene; 0.910 to 0.940 g/cm3) and were really developed for the manufacturing of water tanks, bins, toys and furniture. They can become brittle from oxidation, have lower tensile strength, tend to flex especially on flat areas, can be prone to warpage and are damaged by ultra violet light if they are not UV stabilised.
HDPE (High Density Polyethylene; density equal to or greater than 0.941 g/cm3) is a much more suitable material for manufacturing kayaks. It has high tensile strength, is a stiffer material than LDPE & LLDPE, giving a rigid feel to the boat, has a good level of scratch resistance and good impact strength.
Palm uses a grade of material called Superlinear HDPE Polyethylene (density 0.949 g/cm3) and was specifically developed a number of years ago for the kayak industry in the UK by Matrix Polymers. It has all the qualities of the HDPE above, but the polymer forms more linear chains giving a more crystalline structure which improves strength and durability for the rigours experienced in kayaking environments.
Low Density Linear Polyethylene LDPE:
Used in the manufacture of good quality washing up bowls and water butts. Also used in the manufacture of low grade Sit On Top kayaks and low grade touring kayaks.
Easiest plastic of the three to work with and therefore cheaper to manufacture. Impact resistance, abrasion resistance is significantly lower than MDPE and HDPE. LDPE is not capable of providing the through life performance that even a lightly used kayak will experience.
Cheaper plastics are backed up with cheaper chemistry and the lack of quality UV stabilisers will see the plastic become brittle well before it's time.
There are advertisements in the market place, but there by LDPE moulders where they say HDPE and MDPE are not the right plastics for kayaks. Well sunbeam, the guys testing the limits of their paddling skills in extreme condition only paddle in HDPE and that has been the case since roto moulded kayaks first appeared on the scene. To suggest anything different is to suggest the smog hanging over Beijing is good for your health! China produces a third of the worlds pollution and some of that comes from kayak manufacture using LDPE!
We WILL NOT Supply or Stock kayaks made from LDPE.
The Canoe Shops Group Ltd.