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August 2013

Mattress spring mechanics

This is quite an extensive and advanced Q & A article where we try to get to the bottom of the actual spring mechanics used within particular mattresses. After discussions with a range of spring experts, we shed light on some of the more advanced questions we have been asked.

Lots of questions, and yet there is no available data from the mattress industry to offer any kind of categoric answer. We have made it our mission to get down to the root of these questions and the ones above are just the tip of the iceberg!

Pocket spring mattress hand stitching
Not all springs work the same way so we’ve delved deeper into the mechanics.
  • Is a ten turn pocket spring better than an eight turn?
  • Is a six turn any better or worse?
  • Is the seventeen turn Hypnos Ultrasens pocket Spring significantly better than their eleven turn Ultrasens pocket spring?
  • Does a pocket spring contained within a calico housing offer any benefit to those contained within a spun bond housing
  • Do layers of mini springs on top of a pocket spring unit offer any benefit to the user?
  • What is the optimum number of pocket springs used within a mattress?
  • Is there a table to determine what gauge spring is optimum for particular bodyweights?

Over the years we have received numerous questions specifically asking about the benefits and qualities of a particular spring unit, or whether a combination of springs offers the support qualities suitable for a particular body weight.

As members of The Institute Of Spring Technology we have access to the latest software, the best minds in the field and access to current data we can use to determine whether mattress springs either live up to the associated marketing or not!

ist imageAs the spring unit is the most important part of the mattress it beggars belief that the intrinsic detail of this particular component in a particular product is not explained to you in detail and also, whether the suitability of any particular spring unit is appropriate for you.

However, before we dive in please watch our video explaining how pocket springs work in order to fully digest the complexity of some of the questions and theories below about springs!

All of our calico encased pocket springs, found in our high-end Artisan models are all vanadium coated and this post explains more about that. The data sheet for the vanadium coating is also listed below.

Chemical Composition of Steel WireCMnSiPSCuV (Vanadium)
Percentage Contained0.710.54180.120.0140.1900.5/0.9

Surely a spring is a spring?

Spring design, patent and mechanics count towards a manufacturer’s stable of assets and, therefore, will be subject to intense secrecy. The opinions and comments we give will be based on the data we currently have to hand, the opinion of metallurgist engineers and the opinion of specialised outside sources etc,  therefore, unless the actual manufacturer chooses to disclose data to confirm or disprove what we say – you must take all this within the confines of our abilities to uncover what we feasibly can. However, all responses will be backed up with all available data we used to establish any conclusions.

This section of the site will either be extremely interesting to you or a complete bore! Either way, you can be assured that we are asking these extremely important questions on your behalf. Even if your interest in this subject is minimal, it will be beneficial to you to at least have a handle on the questions you should be considering in relation to your purchase.

To get the ball rolling, the following are general spring questions and in the cases where we require an authoritative response we submitted these to the IST. As a secondary avenue of opinion, we also question a prominent spring manufacturer for their take on the matter. We think we have covered most of the fundamental aspects of mattress spring metrics but would love to hear your comments, questions or responses by using the comments facility below.

Once the basics of spring mechanics have been covered we will then start to dissect the spring mechanics and composition of current models based on our findings to see if they stand up to scrutiny!

What is the basic rule of a pocket spring?

If you have read the articles on pocket springs you will be aware that there are several designs of spring each used by a particular manufacturer and each claiming that their design is the best. All mattress springs are ‘compression springs’ in one form or another with the most basic being a cylindrical tube of coiled wire comprising of a set number of ‘turns’. The individual spring offers resistance to a compressive force applied meaning that when you put a load (you) on the spring making it smaller the spring is pushing back against the load trying to get back to its original shape.

1. Do springs lose their ability over time to return to their original shape?
The reason for this question is to get to the bottom of selecting the right spring for your bodyweight based on correct support and durability.  Theoretically, the heavier you are the firmer the spring you will need to support you. Conversely, lighter body weights will not require such supportive elements. However, when coupled with adequate layers of upholstery it stands to reason that the supportive qualities of spring and upholstery will increase the overall tension of the mattress. We seek to find out the correct balance of spring gauge and upholstery to determine what tension is best for a particular bodyweight.

    • What will be the general deterioration rate over time?
    • Is it better to opt for a firmer spring to take into account any future deterioration?
    • Do springs lose their efficacy within a short period of time and then stabilise – or, is a long term slow process?


2. Which would be the most beneficial shape to be utilised as a pocket spring for a mattress?

There are two basic shapes that are used as pocket springs:
1. The Common Cylindrical Shape  
2. Barrel Shape

3. Does each shape have any particular benefits over the other?
1.If Straight Coil –
2.If Barrel –

4. What are ‘turns’?
Turns are also referred to as ‘Active Coils or Active Turns’. This is the number of coils that make up the spring. In the case of Vi-Spring, they utilise six active turns (The VI stands for Six). These are always based on the straight coil. In the case of Hypnos, they use either ReActive or Ultrasens springs. These are convex barrel shaped springs with differing number of turns – up to 17 turns on their Ultrasens 17. Turns are counted each 360° from the top open end – See image.

spring turns

5. Is there a premium number of active turns for a pocket spring?

6. Would there be a significant difference in support between a 10 turn spring and a six turn spring?

7. What would the difference be?

8. What would be the better unit?

9. Do the turns influence the shape or does the shape influence the turns?

1. The Ultrasens 17 spring (image) is based on a barrel shape and has 17 active turns. Is this excessive or beneficial?
2. Where precisely on this particular spring is the load balanced?
3. Is this design the optimum? Would a 19 turn spring, for example, be any better?

10. Is there an optimum shaped compression spring?
If every manufacturer utilised a six turn pocket spring there would be no conceivable difference between the bulk of all mattresses. Therefore, each manufacturer has to develop their own particular spring unit to offer a viable means of difference. The million dollar question is; which manufacturer currently has the best spring unit and design?

 

What is wire gauge and diameter?

Wire gauge is the thickness of the wire used in the actual spring. The Diameter is how wide the finished spring will be.

Wire gauges used in pocket springs will usually be amongst the following measurements:

      • 1.22mm Softest
      • 1.32mm
      • 1.42mm
      • 1.52mm
      • 1.62mm Firmest

These are standard drawn wire gauges but any thickness can be produced.

The Diameter of springs can also vary and the diameter has a direct relation as to how many springs you can get into a mattress. The larger the spring – the less number of springs can be contained. The smaller the diameter – the higher the number of springs can be contained.

Diameters of springs (cylindrical) fall into the following sizes as standard – Large to Small

      • 62mm
      • 61mm
      • 60mm
      • 56mm
      • 54mm
      • 53mm
      • 51mm
      • 50mm
      • 49mm
      • 48mm


1. Is the difference between diameter and the load they will take important?


2. If Yes: How great would this difference be in real terms?


3. In the case of a pocket sprung mattress (150 x 200) would the difference in diameters actually make that much difference to users support/comfort?


4. Would there be a significant benefit in doubling these springs up in two tiers?


5. If doubled up where does the point of resistance lie? In the centre of each spring or at the top and bottom of each spring – or elsewhere?


6. If doubled up, and based on the above diameters; what would the result be?

[Still working on this..]

Do compression springs offer support and comfort?

Theoretically, the springs should be offering the support and the upholstery offering comfort. However, the support could be seen as subjective to the overall level of comfort. This is to say, if the springs are too firm for the user, then it stands to reason that no matter how much upholstery is used – the mattress can be deemed to be uncomfortable by being too supportive. There is a rule of thumb calculation that the spring should NOT depress by more than 40% of the load applied – ie: inadequate support.


1. From the following, which would be the best construction for the optimum level of comfort and support?

2000 springs of a thinner gauge wire
1500 springs of larger diameter (same gauge)
2000 springs of double layer of 1000 in each tier

Weight differences
1. Is there a spring type/combination that would suit two people of varying body weights say 10 stone and 20 stone?
2. Would a 10 stone person be more comfortable on 1000 springs or 2000 springs if the wire gauge was the same – say 1.30mm?
3. Does the gauge of the wire influence the load bearing – If so by what degree?
4. If yes, what would this be for an average weight of 14 Stone?

We are currently experimenting with the use of layers of mini springs sandwiched between various layers of foam and/or upholstery. The basis of the experiment is to find out whether multiple layers of unattached smaller springs provide a greater element of gradual support than the traditional method of either one or two layers of traditional pocket springs.

We asked:
Using 2 layers of mini springs sandwiched between three layers of High-Density foam to comprise a ‘spring unit’;

      • Foam (2cm)
      • Spring (4cm)
      • Foam (2cm)
      • Spring (4cm)
      • Foam (2cm)

1. This combination totals 14cm.
2. What will be the thesis of support utilising this combination?
3. How much of a difference will this combination be compared to a traditional pocket spring unit?

Summary

We understand there are more questions than answers here on the mechanics of pocket springs, which goes to show just how difficult this area is.  Shrouded in mystery and sometimes no definite answers. This is a long term project and the results of these experiments will be published here as we proceed. If you are a spring mechanic yourself get in touch and help us develop some more detailed answers.

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