How to Choose Your Elastic Cord: Diameter, Material, Shape and Use

The elastic cord, also known as a sandow, elastic tensioner or bungee cord, is one of the most versatile fixing accessories around. It lets you tension a tarpaulin, secure a load, hold a net in place, fix equipment or make an installation safe, all while absorbing movement and vibration thanks to its elasticity.

But not all elastic cords are created equal. Between the various diameters, sheath materials, levels of elongation and available shapes, it is easy to get it wrong and end up with a sandow that is too soft, too stiff or unsuited to its environment. This guide runs through the criteria that really matter so you can choose the right elastic cord first time.

Understanding the structure of an elastic cord

A quality elastic cord is made up of two components:

• the elastic core: a bundle of latex threads that gives the sandow its stretch and its ability to return to its original length;
• the braided sheath: a textile cover that protects the core against abrasion, UV and moisture, and which largely determines how long the cord will last.

The quality of the core makes all the difference between a cord that holds its tension for years and one that goes slack after just a few months. The percentage of latex, the number of threads and the braiding method all have a direct bearing on the strength and behaviour of the sandow. To fully understand these differences in construction, read our article on the difference between single-strand and multi-strand sandow cords.

Criterion 1: the diameter of the elastic cord

Diameter is the first thing to look at, because it determines the tensioning force and strength of the sandow. Put simply:

• 2 to 4 mm: the small-diameter elastic cord, sometimes called elastic cording, suits light-duty tasks: securing covers, arts and crafts, banners, small nets and staking plants in the garden;
• 6 mm: the all-round diameter par excellence, ideal for light tarpaulins, tents, garden shelters and everyday fixings;
• 8 mm: the sweet spot for trailer covers, pergolas, shade sails and regular outdoor use;
• 10 to 12 mm: the larger diameters, made for heavy-duty use: lorry tarpaulins, marquees, event structures and professional load securing.

The rule is simple: the heavier the load to hold and the more frequent the use, the larger the diameter needs to be. A sandow that is too thin will be working permanently at the limit of its capabilities and will wear out prematurely; a sandow that is too thick will be hard to tension and will place excessive strain on the fixing points. To learn more about this, read our guide to the breaking strength of sandow elastics.

Criterion 2: the sheath material

At equal diameter, it is the sheath that sets two elastic cords apart. There are three main families:

The polypropylene (PP) sheath

The polypropylene elastic cord is the versatile, budget-friendly option. Light, supple and available in a wide range of colours, it is perfectly suited to everyday indoor and outdoor use: tarpaulins, nets, camping, workshops and DIY.

The polyethylene (PE) sheath

The polyethylene elastic cord moves up a notch on resistance to abrasion and UV. It is the option to go for when it comes to long-lasting outdoor installations, repeated rubbing and demanding environments such as building sites or transport.

The polyester sheath

The polyester elastic cord offers the best durability over time: excellent resistance to UV, the weather and wear, with a softer feel and a tight braid. It is the go-to choice for professional use and prolonged exposure to the sun.

For marine environments (boats, pontoons, sea spray), there are cords specially designed to withstand salt: our article on marine elastic cords sets out the criteria specific to these extreme conditions.

Criterion 3: elongation, or the "springiness" of the sandow

Not all elastic cords stretch in the same way. Elongation refers to a cord's ability to lengthen relative to its resting length:

• standard elongation (around 100%): the cord doubles in length under maximum tension. This is the classic behaviour of an all-round sandow;
• high elasticity (up to 150% and beyond): the high-elasticity elastic cord stretches further and absorbs jolts better. It is ideal when the fixing needs to accommodate significant movement: tarpaulins exposed to the wind, trampolines and flexible structures.

Lower elongation, by contrast, gives firmer tension and a more rigid hold, which is preferable for securing loads that should barely move at all.

Criterion 4: round cord or flat cord?

The round sandow is the most common, but the flat elastic cord has its own specific strengths: its flat cross-section spreads pressure over a wider surface, which reduces the risk of marking or damaging the items being held. It is particularly popular for securing luggage, fixing fragile objects and any use where the cord passes directly over the material to be protected.

Round cord remains preferable when you need to slide the sandow through eyelets, hooks or tensioners, and for general tensioning tasks.

Criterion 5: the use and the environment

Finally, match your choice to the real-world environment in which the cord will be used:

• permanent outdoor use: opt for a PE or polyester sheath that resists UV and the weather;
• indoor or occasional use: an all-round PP sheath is more than enough;
• repeated rubbing (side rails, edges, metal eyelets): choose a reinforced sheath and check the contact points regularly;
• permanent tension: go for a larger diameter, as the cord will age better working well below its stretch limit;
• frequent adjustment needed: pair your cord with ready-to-use hooked elastic tensioners.

If you are torn between a ready-to-use tensioner and a cord you cut yourself, our comparison of the bungee tensioner versus elastic cord will help you decide based on your intended use.

Reel or cut to length?

One last practical point: the format. The reel is the most economical option for regular users, workshops and professionals: it lets you cut exactly the length needed for each job and make your own tensioners with hooks and end caps. Cord by the linear metre, on the other hand, is ideal for a one-off need or a specific repair, with no surplus stock.

In both cases, always cut the cord slightly shorter than the distance to be covered: a sandow only holds properly when it is working under tension, with moderate stretch relative to its maximum capacity.

Mistakes to avoid when choosing

• choosing on price alone: a cord whose core contains little latex goes slack quickly and needs replacing often;
• undersizing the diameter: a sandow that is permanently working at its limit loses its elasticity prematurely;
• ignoring UV: in full sun all year round, an unsuitable sheath degrades and the core soon follows;
• neglecting maintenance: a regular check of the ends, hooks and rubbing areas significantly extends the cord's lifespan. Our full advice is in the article on care and maintenance of elastic cords;
• stretching the cord beyond its capacity: maximum elongation is not a target but a safety limit.

FAQ: choosing your elastic cord wisely

What diameter of elastic cord for a trailer cover?

An 8 mm diameter is the benchmark for trailer covers: powerful enough to hold the cover under tension on the road, yet still easy to tension by hand. For lorry tarpaulins or heavy-duty use, step up to 10 mm.

What is the difference between a sandow and an elastic cord?

None: "sandow" is the everyday name for the elastic cord, inherited from Eugen Sandow, an athlete famous for his spring exercisers. The terms elastic cord, bungee cord, elastic tensioner and sandow all refer to the same family of products.

Can an elastic cord stay outdoors all year round?

Yes, provided you choose a suitable sheath: polyethylene and polyester offer lasting resistance to UV and the weather. A standard polypropylene sheath, however, is better suited to occasional or sheltered use.

How do you fix an elastic cord?

It depends on the use: crimp-on or screw-on hooks, end caps, sewn loops or specific knots. Hooks fit easily onto a cord cut to the required length, which lets you make perfectly tailored tensioners.

Why has my elastic cord gone slack?

Three main causes: a core low in latex, permanent tension close to the elongation limit, or prolonged UV exposure with an unsuitable sheath. A quality sandow, correctly sized, holds its tension for years.

In summary: the right elastic cord is the one that matches your use

Choosing an elastic cord comes down to answering five questions: what load (diameter), what environment (sheath material), what behaviour (elongation), what shape (round or flat) and what format (reel or by the metre). By combining these criteria, you get a sandow that lasts, protects your equipment and stays a pleasure to use day to day.

All our elastic cords are made with a quality latex core and available in a wide range of diameters, colours and formats. And if you are unsure which option best suits your project, our team will be happy to advise you.