A Comprehensive Guide To Plastics Used To Make Kayaks
There is basically only one "polyethylene" (PE) used to manufacture rotationally moulded kayaks, but that PE plastic comes in many grades. These grades are generalised as HDPE (high density) MDPE (medium density) and LDPE (Low density) - density refers to the number of molecular bonds within the plastic not the mass/weight of the plastic. The more molecular bonds in the plastic give a stronger, stiffer, puncture resistance, abrasion resistance and better memory. Memory is the quality whereby the plastic remembers the shape it was originally moulded in - this extends the useful life of the product. The more sophisticated plastics like HDPE have the best chemistry and quality control with higher standards of UV stabilisers and plasticisers.
HDPE is more expensive to buy and mould than MDPE and LDPE.
MDPE is more expensive to buy and mould than LDPE.
LDPE is the least expensive PE to buy and mould.
High Density Linear Polyethylene HDPE
HDPE is the PE of choice for kayaks that will be subject to extreme use on white water, sea kayaking and offshore angling.
HDPE is a more expensive and more demanding to mould but the strength and through life results are the best. HDPE moulds at higher temperatures and is less affected by high temperatures when the kayak is strapped onto a roofrack or stored when LDPE kayaks will start to deform.
There is a trade off between strength and cosmetic appearance when HDPE is used to manufacture stronger kayaks. LDPE will provide a smoother look because it stretches easily where HDPE decides to hold its moulded shape and is very slightly less smooth.
Drag the kayak up the beach once and they will look the same but the HDPE kayaks will still be stronger.
Medium Density Linear Polyethylene HDPE
Is the PE of choice for kayaks that will be paddled by mere mortals as opposed to those that throw themselves off 60 foot waterfalls or paddle around the poles. Most manufacturers mould kayaks with MDPE.
Low Density Linear Polyethylene LDPE
LDPE has found favour with the commodity kayak manufacturers manufacturing in China where the product has to hit a particular price point. A commodity kayak manufacturer uses LDPE, copies someone else’s design and manufacturers kayaks under environmental and employment conditions we would not find acceptable in the UK. The resulting kayak hits the desired price point, and is often pleasing to the pocket of the first-time buyer.
LDPE or LLDPE is the easiest plastic of the three to mould kayaks from. It is the cheapest to buy and moulds at lower temperatures but strength, impact resistance, abrasion resistance, UV stability and memory are all significantly lower than MDPE and HDPE.
Canoe Shops Group wants everyone to be able to afford to go paddling but will tell it like it is. It has taken us more than 5 years to source a range of entry level kayaks manufactured in LDPE that we were prepared to retail. In more ways than one there is still a lot of Junk coming out of China so buyer beware! Having satisfied ourselves that Enigma Kayaks are as good as it gets in LDPE we are able to offer them for sale in the UK. Our additional guarantee to our customer is should they wish to upgrade to a more sophisticated product then we would part exchange a Enigma Kayak because we know about its manufacture, but we will not part exchange other LDPE kayaks we know nothing about.
For the more technical minded we refer to observations made by one of the UK’s top kayak moulder who moulds the highest quality kayaks:
"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."
Director of Dagger & Wilderness Systems Kayaks UK