Know your GSM timestable

GSM is the one thing mattress manufacturers do not want you to know! And once you do, you’ve got the upper hand. We promise!

WSC 300GGSM stands for ‘Grams per square metre’. It refers to the actual weight of a particular upholstery component used within the mattress. It is a measurement used by all mattress manufacturers when purchasing upholstery and used as a basis to establish the quality of a particular mattress.

It is the weight of a square metre of material and it does not matter what type (wool, polyester, horsehair ) or how deep or fluffy, or how thin, or how bouncy the actual weight of a metre of the material remains a constant.

It is also the weight of the entire depth of various upholstery components used directly on top of the springs and this is known as the ‘combined upholstery weight GSM’.  This is the weight in One Square Metre of all upholstery used in your mattress. If you know this GSM figure – you would be able to tell which mattress is better than another without even lying on it.RPC 800

How So?

Take wool as an example.

  • This comes in weights of 300 GSM / 600 GSM / 1200 GSM.
  • You see two mattresses advertised as having wool upholstery.
  • One has 1200 GSM wool as the upholstery. The other has just a miserly 300 GSM.
  • They are both selling at £500.

Unless you know which mattress has the 1200 GSM wool, you will never know which was the better-built mattress for the same price.

Bonded wool and cotton

Is it really important to know GSM?

Absolutely! In fact, so important for you to know it is very rarely mentioned in any mattress description you will see in the store or on the internet. This is the one thing manufacturers do not want you to know or ask about, and they rarely divulge this to the retailer never mind the consumer! Once you read the explanation below you will soon see that on the majority of mattress specifications and descriptions of a mattress from the majority of retailers this blatant omission becomes evident by it’s very absence.

So what is GSM in simple terms?

Let us look at a typical real life example. This is a description and specification of a mattress sold by Dreams [May 2013: Lincoln: Kingsize Mattress: £1429.00: Product code: 131-00199] – No longer listed [Mar 2014]

The product description states:

‘If you’re looking for the ultimate in comfort with a luxurious feel, then our Lincoln deluxe pocket spring mattress is the ideal choice. Made exclusively for Dreams with superior craftsmanship and high-quality materials, our Lincoln mattress offers you extra firm ergonomic support with 3500 pocket springs, generous pure new wool and cashmere upholstery and finished with the finest quality Belgian damask. Our Lincoln mattress is double sided and features stitched handles to allow you to prolong the life of your mattress with regular turning. The supreme quality of our Lincoln mattress makes it durable and highly desirable as an investment in a great night’s sleep.

Advertised Specifications:

3500 pocket spring –
Key fillings: polyester/cotton – Pure new wool and cashmere Woollen – Hand-tufted mattress panel Double-sided
Comfort grade 2 – Firm

What you should be trying to do is to see where your money is going.

We know that it contains 3500 springs fair enough, but what about the upholstery as the fillings? The description states quite clearly “generous pure new wool and cashmere upholstery”  What exactly is deemed to be ‘generous’? 

The specification tells you that the key fillings are polyester/cotton, pure new wool and cashmere, but how you do you actually know that this is true? Don’t just take the above description as being what you ‘think’ you will be getting.

The above is all the information this particular retailer decides to give you. But remember, they are asking about £1400 for this particular mattress so you should absolutely need to know where your money is going?

How can I tell what is in a mattress?

As a consumer, you need to ask the following five questions to this particular retailer or indeed all retailers and this will explain in detail what you are up against.

1. What is the combined upholstery weight?

The combined upholstery weight is the total weight of all the fillings used in a square metre of the mattress upholstery. If we take for granted that for this retail price you should be looking at around 3000 GSM of premium upholstery this description tells you very little. In reality, it could be a paltry 1200 GSM and you will have no recourse because you weren’t told otherwise.

2. What is the GSM of the polyester?

Polyester is amongst the cheapest mattress components you can get. Usually, given names like premium white fibre or anti-allergenic white fibre, it is still polyester and it is still cheap. If this component forms the bulk of the upholstery you are paying top whack for a cheap mattress. However, we don’t know for sure because the actual weight is not given.

Pollyester 800G

3. What is the GSM of the cotton?

Take note that on the description given, the cotton is forward slashed with the polyester. It is quite rare for cotton to be used as a stand-alone component (it is not fire retardant) and usually forms part of a blend. In this case, it is likely that the polyester/cotton is a component known as RPC (rebound poly cotton) not a bad component but not premium either. This comes in weights of 300 GSM / 600 GSM / and multiples thereof. As no GSM is given you can be buying a paltry 300 GSM or an acceptable 1200 GSM. You don’t know!

4. What is the GSM of the pure new wool?

Again, same story. Pure new wool is amongst the most expensive components within a mattress. The description has again forward slashed this with cashmere. A reasonable person may assume that these are separate components but are they? Wool is often used as a blend (usually with cotton on high-end mattresses) and 1200 GSM is an acceptable weight obviously if backed up with other substantial fillings. There is a component known as WSC (wool, silk, cashmere) and comes with a weight of around 300 GSM. This weight is neither use nor ornament unless again it is supplementary to a substantial level of upholstery.

If you see the description of wool, silk and cashmere on a product description you can assume it is there to make the mattress look as though it is packed with premium components. However, without a gsm weight attached the actual weight could be so minimal it is worthless.

5. What is the GSM of the cashmere?

Cashmere is a premium component and this is more than likely part of a blend. The description is a little misleading as like the pure new wool above it is forward slashed with another product. Being part of a blend, say with pure new wool you will then have to know the ratio. Cashmere is phenomenally expensive and so don’t be surprised if the ratio of cashmere to wool is as little as 5% of the entire GSM. The fact that it can legally be included within a product description has more value than the component itself.

White cashmere

And that’s it. A little scratch on the surface which from a simple description and basic specification of a mattress that is retailing at £1400 or so opens up a complete minefield of questions and doubt. This is a classic example of why you are going to find purchasing a mattress so ridiculously hard, frustrating but completely unnecessary.


There is no legal requirement for a manufacturer or retailer to divulge the contents by weight to you but that does not make it right. Looking at the description above even we cannot tell you what the weight and breakdown of the upholstery layers are – they are complete unknowns and without you knowing what these are it becomes quite impossible for you to do any kind of comparison to other models. And this is the sole reason why this shameless practice is carried on.

You may be thinking that all of this is completely mind bending and complicated it is initially  but it is absolutely essential you understand it otherwise, you will be at the complete and utter mercy of the manufacturer and retailer. The moral to all of this is not to take any description at face value. The least you need to know is the ‘grams per square metre’ of all components used within the mattress. If a mattress description tells you it is filled with ‘luxurious horsehair’ or has ‘sumptuously soft silk’ you need to be asking but how much?

This is just the starter post on understanding what it will take to find your perfect mattress. As with the Dreams Lincoln example above you have to know how to do comparisons between different models to see which is giving you the best mattress for your money. For us, it has now become second nature, and we know this will be a considered exercise for you. There is absolutely no need to panic!

Once you understand what to look for you will be skimming through descriptions like a demon and quite enjoy spotting the misleading and dubious specifications you come up against. There really should be no reason why you should go to these extraordinarily long lengths having to play Sherlock Holmes and phoning manufacturers to ask the necessary detail on upholstery before you hand over hundreds or even thousands of pounds for your mattress. To be honest, it’s absolutely disgraceful that you will have to do this to compare.

The GSM value of upholstery is the one thing 99% of ALL manufacturers do not want you to know.

We hope that manufacturers and retailers will eventually tire of the calls and questions and list their products the same way as food manufacturers do with a completely itemised summary showing component and weight.



View Comments
  • Haq says:

    Hi there,

    I must confess I have spent several hours now reading your website and I am awed by your knowledge and expertise. I went into a bed shop today and I had to teach the so called “expert” a thing or two (politely I must add, although this wasn’t my purpose for reading). So hat’s off to you!

    Now my q: What would you say is a good GSM for a double polyester mattress topper (disregarding the cost factor)?

    I have a natural filling duvet at the moment and I don’t like how everything seems to move around inside, hence why I’m going for a synthetic material.

    Would love to hear from you!
    Sorry my weight is 9 stones and my mrs is 7 stone.

    Hi Haq. Unfortunately most toppers do not have an associated gsm weight attached. I personally use the Ultimate Microfibre from Duvet and Pillow Warehouse coupled with a Feather and Down one. It may be worth looking at using Duvets as a topper (Marks and Spencer tend to have a good fill ratio).

    Toppers are a personal purchase and I’m afraid it can be trial and error before you settle on the right combination. John and Ryan

  • Mac says:

    Firstly many thanks for a great site – after weeks meandering around many retail sites I was no nearer to shortlisting but having read your various articles I am now in a position to understand what I am getting for my money – Thank You
    A couple of questions if you don’t mind –

    1. When considering two sided mattresses where the manufacturer gives a breakdown of the upholstery layers are the weights given for EACH side of the mattress?

    Hi Mac, for ease of reference, I will answer your questions in order. When a manufacturer refers to an upholstery breakdown, this should be given by GSM (grams per square metre) and therefore, will refer to the overall upholstery.

    2. I have been looking at a couple of Vi Spring Mattresses (bottom of the range) – The Elite Double and the Baronet Superb. The latter is £300 to £400 more expensive, has a similar number of “calico” springs and like the cheaper mattress wool and cotton upholstery – however despite being considerably more expensive it has a Combined Upholstery weight of 2,200 GSM compared to the cheaper mattress having a Combined Upholstery Weight of 3,150 GSM – I would have thought a similar mattress with 50% higher CUW from the same manufacturer would be more expensive not cheaper – What am I missing?

    The Baronet Superb does have less of the listed Bonded Platinum Certified British Fleece Wool & Cotton and the Blended Platinum Platinum Certified British Fleece Wool & Cotton than the Elite, however, it does have a pad of Horsehair needle teased on to Hessian between the spring units and the Fleece Wool & Cotton upholstery listed. Horsehair is an expensive element to have in any mattress and although there is no specified GSM for this element, I would estimate it to be at least 1000 GSM and as a consequence, the price for the Baronet Superb is higher.

    3. Apart from the Vi Springs above I have been looking at the John Lewis Naturals mattresses ( the 4000 @ £700 (albeit 1 sided) and the 6000 (2 sided) @ £1,100. The spring count on both of these is way in excess (by a factor of 4 or 5) of the 1,050 and 1,116 of the VS mattresses – should the relative low spring count on the VS mattresses be of concern when it comes to comfort? I am a lightweight – 10 stone.

    A spring count of over a 1000 in a standard double mattress is more than sufficient to deal with your body weight. The John Lewis Naturals Mattresses are manufactured by Harrisons and in addition to the usual springs they have additional layers of mini springs, which are exclusive to Harrisons. The number of mini springs is likely to be at least double that of the standard encased springs, they are exclusive to Harrisons and a 1000 or over is sufficient.

    Finally I have read your comments on one sided mattresses but given my weight and the fact that I would prefer to keep the spend below £900 I wonder whether what appears to be a well constructed JL Natural 4000 @ £ 700 might meet my needs or is there good reason to spend the extra and consider your Artisan Naturals @ £985 – BTW Where are your Artisan Naturals mattresses made?

    The main benefit of a double sided mattress is the longevity it provides and whilst an initial spend of £700 may seem reasonable, if you are unable to turn the mattress, even with your body weight, it is likely that you will experience a greater degree of settlement, which may in turn mean a replacement is needed sooner making the saving academic. The choice is yours, although I would recommend a double sided mattress, even if your choice is not one of ours. All our mattresses are made in Yorkshire. I trust that the above responses clarify matters for you. Kind regards Mike.

    Any observations / advice you are prepared to offer would be appreciated.

  • LadyGeek says:

    At last; seeing everything in print that has long been on my mind but I didn’t know the right Qs to ask, so many thanks for that. Btw why no mention of wool bedding on your website? I’m particularly considering a pure wool mattress topper. Since I reverted to wool blankets I’m a very happy bunny and a snuggly topper would be woolly heaven. 🙂

    Hi LadyGeek, We are always updating our site and posts but bedding is really its own site entirely and we are the mattress geeks! Bedding breaks off into interior design and fabrics rather than mattresses/bed design. We do discuss the GSM and breakdown of fabrics but stop short at bedding. Bedding is so subjective and not very technical which is why we don’t have a specialist section on it. Glad you’re snuggly in your woolen heaven!

  • Katy Snifty says:

    Hi Guys,

    Love the website, I now feel like I am on my way to a BA in Mattress science.

    I was looking at the Vi-Spring Dartmoor at John Lewis and was hoping you could guide me as to it’s quality. It retails for £999.

    I asked for the specification breakdown and they sent me this:

    |Panel | |
    |Border |21cm deep, wool filled (WIBW-020), |
    |depth/backing |spunlace backed (SL70-020) |
    |Vents |Silver |
    |Side stitching |2 rows |
    |Rods |2 Perimeter (Removed) |
    | |Europe = 2 inner rods |
    |Spring unit |Set B: 90 x 200 = 780 |
    | | 135 x 190 = 1116 |
    | | 150 x 200 = 1326 |
    | |Options: Soft Medium Firm|
    | |Xfirm |
    | |Gauge: 1.42mm 1.52mm |
    | | 1.73mm 1.83mm |

    |Border filling |Wool (WISI-015) |
    |Upholstery – sleep|1000g Bonded Rebound wool/cotton |
    | |(BRP10-size) |
    | |900g Layered Rebound wool/cotton|
    | |(LRP09-size) |
    |Upholstery – non |n/a
    |sleep | |
    |Tufts/length |Felt (TUFF-NATL), cotton jiffy tufts|
    | |(TUFS-18) |
    |Packaging |Multi-purpose bag (POMP-size) |
    | |152 & above to be boxed (BOXM-Size) |
    | |Clear tape (TAPE-50F) |
    |Weight |Excluding packaging – Soft:|
    | |kg/m2 |
    | | Medium: |
    | |kg/m2 |
    | | |
    | |Firm: kg/m2 |

    I also asked which model it was closest to in their normal range and they said it was nearest to the “Elite” which has a spring count of 1254 and similar upholstery. But the Elite is almost double the price! What is the difference to justify such a change in price?!

    What are your thoughts on this? Does it seem like good value for money? Seems like it’s mostly wool that’s used which will be good for natural fibre ratio, but wool may compress over time if not used with something else, perhaps?

    Best wishes and thank you for your knowledge!

    Hi Katy,
    Thank you for the compliment in respect of our site. Vi-Spring is a reputable manufacturer of mattresses.The first thing I would say with regard to both the Dartmoor and the Elite is that with there only being wool as the major upholstery element, they are likely to feel very soft. The main difference between the two is that the Elite has a total of 3150GSM in upholstery, whereas the Dartmoor only has 1900GSM, so I fail to see how the latter can be compared to the former. If you are not looking for a soft feel mattress then I would steer clear of these.

    Unfortunately, without details of your body weight and preferred feel, I am unable to suggest alternatives. If you would like to provide this information to our office by telephone, you could then obtain more specific advice as the suitability of mattresses in our Artisan range, some of which are comparable to some Vi-Spring models. I trust that this helps, kind regards Mike.

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