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Fabrics - GSM vs Grams Explained

Understanding Horse Rugs - 'Gsm' vs 'Grams' vs 'Deniers'

Do you get confused when comparing ‘gsm’ to ‘grams’ & ‘deniers’ when looking at the specifications of horse rugs? Well you are not alone! Actually 'gsm' and 'grams' are used interchangably and refer to the same thing.

We are often asked if a 300gsm polar fleece horse rug is as warm as a 300gram poly filled turnout rug.  The short answer is no.  Like all industries the horse rug world uses terms and jargon that can be confusing, leaving you overwhelmed and uninformed.  Let us try to dispel some of the mystery and confusion of horse rug terminology.


Put simply, GSM or 'grams per square metre refers to the actual weight of one square meter of that particular fabric. If you cut one square of meter of fabric and weighed it, the resulting weight would be the 'gsm' of the fabric.   However, the weight or gsm  has no relevance to the warmth provided by the fabric.  The properties of the individual fabric and composition of the materials used are what make a difference to the warmth of the horse rug.  For example, our paddock ripstop rug is made from 300gsm poly cotton,  and certainly are not as warm as our 300gsm polar fleece.  At 410gsm the Caribu Enduro mesh rugs are a  'heavier' gsm than both the ripstop and polar fleece rugs but are not considered 'warm' at all.  So a higher GSM usually means a thicker or stronger fabric.


The gram or weight measurement of poly filled rugs such as the Caribu Alpine turnout rug range, refers to the weight of the poly fill per square meter, but serves a different function to the weight of fabric.  Polyfill is an insulation fibre (like inside a pillow) that creates an insulating pocket which traps body heat generated by your horse in turn keeping the horse warm.   The more poly fill in a rug the bigger insulating pocket is created to trap the warmth.  Think of it like a doona or quilt on your bed.  A heavier filled quilt is much warmer and better to snuggle under in the cold of winter than a light filled one.   

Comparing Horse Rug Weights

Comparison of polyfill lining 300grams vs 200grams

Getting back to horse rugs, a 200gram poly fill rug is going to be warmer than a 300gsm wool rug because the poly fill will trap the horse's natural body heat, warming the air caught around the horses body, in turn keeping him warm.   We know that in cold climates a wool jumper is a good base layer but a filled 'puffy' jacket or old school parka, will be much warmer thanks to the insulating air pockets of the poly fill.    The same principle applies to winter horse rugs.

This leads to another question : how much poly fill should I have in my horse's rug? We have more info about polyfill here.


In turnout rugs ‘denier’ also comes into the equation. The thickness of the individual thread used in the yarn weave, is referred to as the denier. Essentially the higher the denier number, the stronger the material. Commonly in 600D, 1200D and 1680D - the higher the number, the thicker and stronger the weave. The insulation difference between the three deniers is negligible and shouldn't  really play a part in comparing the warmth of one denier vs. another.   We have more info about deniers here.