What’s Inside Your Mattress | GSM Explained

To make sure you’re equipped with all the right knowledge when shopping for your new mattress, take a look at our guide covering what you need to know about GSM and natural fibres.

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What’s Inside Your Mattress?


Grams per Square Meter (GSM) is something mattress manufacturers and retailers do not want you to know when buying a new mattress. But, once you know and understand why GSM is important, you’ve got the upper hand in finding out precisely what’s inside your mattress and whether or not the mattress is worth the money you are paying. We reveal why the retailers and manufacturers hide this detail and how you can find out what’s inside your mattress—helping you not waste money.

Unfortunately, most mattress manufacturers and retailers withhold essential information regarding the design and construction of mattresses. Hopefully, this guide will remind you always to ask, ‘What’s the GSM of the natural fillings in this mattress?’.

You may have never seen the reference GSM before when shopping for a mattress, which proves how tight-lipped the mattress industry is. So let’s dig a little deeper to show why you need to know the GSM.

natural mattress fibres


What is GSM?

Grams per square metre (GSM) refers to the weight of a particular natural fibre used inside the mattress, measurement used by mattress manufacturers when purchasing natural fibres, and a basis to verify the quality of a mattress, for example, the more GSM of high-quality natural fibres in a mattress indicates a higher quality item.

GSM is the weight of a square metre of fibre, and it does not matter what type (White Fibre, Wool, Horsehair, Alpaca, Mohair) thick, thin, springy the fibre is, the exact weight of a metre of the fibre remains the same. So the simple fact is if you don’t know the GSM, you have no way of determining if the mattress you want to purchase is worth the money, but by knowing the GSM, when comparing mattresses, you will be able to tell which is better than the other without even testing them.

wool natural mattress filling

Is the Quality of the Mattress Dependant on the GSM?

Mattress retailers hide the GSM because they don’t want you to make comparisons between mattress brands and models. Without this information, you will struggle to compare and choose a new mattress correctly. This way, saleswomen and men can promote finance, discounts and other sales methods to you until you decide on whichever mattress you think is the best, emphasising the word ‘think. Of course, it would be better to know which mattress gave you the most value for your money in an ideal world.

Take cotton as an example
  • Cotton comes in weights of 650GSM / 1250GSM
  • Two mattresses are displayed as having cotton fibre
  • One has 650GSM cotton, whereas the other mattress has 1250GSM
  • They are both retailing at £1000

Unless you know which mattress has the 1250GSM cotton, you will never know which mattress is the higher quality mattress but you will pay the same price.

Is it Essential to Know the GSM?

Yes, it is! The mattress fillings are the most costly part of your mattress, and so you must know that what’s inside the mattress is worth the money. This is why GSM is rarely ever stated by retailers, online stores and manufacturers, as it’s the one thing they do not want you to ask or know about, so be cautious of mattress stores that say to you, they don’t know.

wool mattress

What GSM Should you Look for in a Luxury Mattress?

When buying a new mattress, make sure that you choose the one with the greatest amount of high-quality natural fillings. Higher GSM of fillings will ensure settlement, indents and body impressions do not alter the mattress over time and provide significantly more comfort and support.

The points below will illustrate the minimum you should expect for the overall total GSM for mattress price points.
  • 4250gsm
  • This should be a minimum of 85% natural fibres
  • 4850gsm
  • This should be minimum 95% natural fibres
  • 5000gsm
  • This should be 100% natural fibres
  • 6350gsm
  • This should be 100% natural fibres

If a retailer’s prices are higher with less GSM or natural fibre content, you should ask them why? And don’t let them give the speel of GSM is not important or their costs are higher because of the springs they use or the handcrafting is expensive as all high-end luxury mattress brands have these same costs for springs, labour and mattress ticking. It’s the fillings that will make the mattress more expensive so for example:

Mattress 1 is priced at £3500


  • 5400 (fillings include Alpaca, Wool, Horsetail, Organic Flax)

Natural fibre content

  • 100%

Outer cover

  • Chemical free cotton cover

Rows of side-stitching (handcrafting)

  • 4


  • 2000 calico springs


Mattress 2 is priced at £2999.99


  • 6350 (fillings include Alpaca, Bamboo, Mohair, Horsehair, Wool, Cotton, Organic Flax)

Natural fibre content

  • 100%

Outer cover

  • Chemical free cotton cover

Rows of side-stitching (handcrafting)

  • 7


  • 13500 patented micro springs


…Because the retailer selling Mattress 1 has a much higher markup. By seeing the above examples, it is clear that mattress 2 is superior to mattress 1 as it has more gsm of fillings, more rows of stitching (meaning more handcrafting), the same outer cover and lastly, even the springs cost more. But, without knowing the GSM, you would not be able to make an educated decision on which mattress is better.

pocket spring unit

How Much do Natural Fibres Cost


  • Very expensive
  • Low supply chain


  • Very expensive
  • Low supply chain


  • Very expensive
  • Good supply chain


  • Very expensive
  • Good supply chain


  • Very expensive
  • Low supply chain


  • Expensive
  • Low supply chain


  • Expensive
  • Good supply chain


  • Expensive
  • Good supply chain


  • Average price
  • Good supply chain


  • Average price
  • Good supply chain

Organic Flax

  • Average price
  • Good supply chain


  • Average price
  • Good supply chain


Once you understand GSM and why it’s so important, you will know what to look for when reading through mattress descriptions. We hope that all mattress retailers will eventually list their products the same way food corporations do, with a detailed summary showing components and weight.

There really should be no reason for the necessary detail on what’s inside your mattress before you hand over thousands of pounds isn’t already given to you so you can make a fair comparison.

At Winstons Beds, we are entirely transparent and list all of our mattress fillings GSM so you can make an educated decision on which mattress you want and whether you believe it’s worth the money you are paying.

Frequently Asked Questions

Natural mattress fillings are either animal or plant fibres, for example, Bamboo, Alpaca, Wool, Coir, Cashmere, Hemp or Latex.

They significantly more responsive compared to synthetic fibres. They're far more breathable and will outperform synthetic fibres in nearly every sense. However, just like synthetic mattresses, natural fibres do have their flaws.

Natural fillings are renowned for indents and settlements. These are entirely normal, however, can cause some discomfort for people until the mattress has wholly settled. Therefore, at Winston's we ask for customers to allow 8-12 weeks for the natural fillings to settle.

When shopping for your mattress lookout for the terms' contains wool' or 'contains natural fibre'. Before purchasing a mattress advertised in this way you need to find out exactly how much of the filling is wool or other natural materials, as some mattresses advertised as containing natural fibres contain as little as 1%. Therefore, you need to know your GSM in order to see whether you're getting good value for money on your purchase.

Natural mattress fillings will usually be found in the more luxury mattresses in the high end mattress market.
Blending fibres can come in hand when using natural fillings such a bamboo, as the cotton will give the bamboo its height, but also allowing for the bamboo to continue to do its job as a natural fibre.

However, it does not always benefit you to opt for a blended fibre mattress. It is more commonly being used as a marketing trick as retailers are being able to list their mattress as containing more wonderful fillings, when in reality the fillings are not providing extra comfort and support to the mattress.

If you do opt for a blended fibre mattress, make sure to choose one that has less than or a 50-50 ration of natural to synthetic materials.

This should then allow you to still feel the benefits of the natural fillings.

Stay away from a mattress which does not specify the split between the fillings as many will describe it as being a blend but will contain less than 1% of natural fibre fillings.

For example, descriptions of a mattress filling layers could be characterised as Alpaca, Horsehair, Wool, Cotton, Cashmere, Polyester and Silk indicates it's a blended pad. However, with them not disclosing the percentage of each fibre they're likely to be putting the majority of the cheaper fibres in the mattress.
The GSM is how much fibre each mattress has inside of it. This will help you work out how long the mattress is likely to last you as well as the level of comfort it will provide.

The GSM also tells you the weight of the upholstery layers, for example, let us talk about polyester as this is one of the most commonly used mattress fillings amongst retailers.

Now if the mattress states it contains 'Polyester' or 'White Fibre' both of which are the same thing, however, they don't supply you with the GSM then you have no idea as to whether it contains 100GSM or 1200GSM. This has a significant difference in support, comfort level and price.

The goal with Grams Square Metre is to get the highest GSM for your budget, which is something that Winston's pride ourselves on.

At Winston's we provide mattresses with the cheapest cost per GSM, meaning your Winston's pocket spring mattress will be full of high-quality fillings that will provide comfort and last much longer than the thinner layer mattress on the market. As well as being much friendlier to your bank accounts than the other mattress retailers on the market.

At Winston's unlike most entry-level mattresses under £1,000, contain natural fibres, compared to other retailers whose entry levels under £1,000 mostly contain synthetic fillings which, then change to natural fibres when over the £1,000 budget.

Winston's wins on GSM and quality of the GSM in their mattresses and lowest price per GSM.
After working out the amount of fibre that is in your mattress the next step you need to figure out is whether the fillings are synthetic or natural fibres.

Knowing this will allow you to see if the price advertised for the mattress is worth it. It will also give you an idea of the level of quality of the mattress, as synthetic fibres are much cheaper than natural fibres, however, beware that retailers will try to charge higher prices for synthetic fibres as it is the mainstream filling.
Synthetic fibres are human-made materials such as Solotext, Memory foam, Polyester and White fibre.

They're significantly cheaper than natural fibres, so they're usually used in entry-level models. They retain much more heat than natural fibres, especially foam products like memory foam, which can cause issues with night sweats and over overheating. They also have a shorter shelf life, and therefore high-quality natural fibre mattress can usually be better value for money.

Anybody who suffers from night sweats or hot flushes preferably should stay away from synthetic mattresses.
At Winston's, you will receive the best value for money anywhere in the UK for a high quality mattress, whether online or in a physical store.

If you can find the same spec mattress at a better price, we will not match it but, we will beat it by offering an additional 10% discount.

Below are tables that demonstrate what you should expect from a mattress based on the price you pay. The first table shows what you will get at Winston's online store and the second table shows what to expect to pay at other mattress retailers.

There is a massive difference in expectations on pricing and mattress quality between Winston's and other major mattress retailers. The tables below are there for you to see for yourself, that Winston’s does not only offer the better value for money based on GSM, but we also provide the best value of money for mattress spec. This is because, at Winston's, we believe everyone deserves a comfortable and supportive night's sleep.
Under £500 - The very best you will get at this price is a 13.5 gauge open coil a layer of thin polyester or a solid foam mattress, with a short shelf life.

£500 - £799.99 - Entry-level spunbond springs with little form of synthetic upholstery. Mostly one-sided mattresses.

£750 - The most basic pocket springs unit with 800 – 1000 count. Little amounts of filling other than foams and synthetic materials. Two-sided mattresses.

£1000 - Gets you away from most low range mattresses and into the mid-range pocket spring models.

£1250 - A decent pocket sprung mattress with little natural fibre content.

£1500 - Most manufacturers mid-range models with natural fibres should be available.

£1500-£2000 - Potentially gets you a handmade mostly natural fibre quality mattress.

£2000+ - Expected to get a 100% natural fibres as well as a traditional hand made mattress.

£5000+ - A bespoke handmade mattress, with a high spring count ensuring they use the world's most luxurious and best natural fibres available on the market.
Know your GSM; this is essential to you finding a good mattress at the right price, if the retailers are keeping the GSM close to their chest then go to another retailer.

Know your fillings; you need to know what's going inside your mattress, remember natural fibres are the more expensive luxurious option.
Pure fibre is much better than mixed fibre, so if you're looking at a mixed fibre mattress, then make sure to find out the GSM, to ensure you're getting the best value for money.

When it comes to memory foam mattresses, you still need to know what's inside of them. However, this is not decided by GSM and goes by the depth of foam layers. When you know the depth of the foam, you will be able to figure out what you're getting for your money.
For example, a 1cm memory form layer will compress almost immediately without much weight, on the other hand, 5cm or 7cm layers of foam will offer much more comfort and will be able to hold more weight, therefore, providing more support.

Foam does not last as long as latex or natural fibres and therefore means you need to make sure you have sufficient depths of foam to get the most value for money.
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Published: 11th November 2020 (Updated: 13th August 2021) | Graham