May 13, 2019

Wool Interlock at HumBird

The 2 Different Wool Interlocks Offered by HumBird.

The question may logically come up, or perhaps it already has:

Why does HumBird offer two different types of wool interlock?

After trying many different interlocks over the years, both HumBird and HB customers enthusiastically embraced the option of two different types. This is gsm after the fulling process.


HumClassic was carefully developed from HumOriginal to be a middle weight interlock with properties of a higher weight. While thinner, it is tightly knit to offer great protection without thickness. The tight knit also imparts a greater resilience on the fabric at places of high stress, like seams and knees. It is a lighter weight, tigher knit, year-round favorite. HumClassic comes in at between 580 and 680 gsm. As with all interlock brands, different colours (dye) react with the wool differently to produce a fabric of different weights.


HumRugged was developed in response to those customers looking for a heavier weight interlock. It makes especially good overnight diaper covers, and can be used year-round as shorts or capris in warmer weather and trousers in cool weather. HumRugged’s gsm ranges from 715 to 770 gsm, again depending on the reaction with the dye. All HumBird GSM measurements were scientifically measured by the mill using multiple samples, a round GSM cutter, GSM pad and a calibrated scale.
HumClassic Seam
HumRugged Seam
HumRugged Seam


Here is some technical information on GSM that some of you may find interesting.

First, What is GSM?
GSM stands for grams per square meter. Fabric GSM means the weight of one square meter fabric in grams.


How is GSM Calculated?
You can calculate GSM for woven and knitted fabric using one of the following methods.



1. By using the testing instrument (GSM cutter and weighing balance)
The standard method of measuring fabric GSM is using the calibrated GSM testing equipment. For testing or measuring the fabric weight, one needs a
  • Circular GSM cutter which will cut an area of fabric 1/100 of a square meter (100 cm2)
  • One digital weighing balance
  • Fabric sample cutting pad

You then take the fabric specimen from different parts of the fabric roll across the roll length and different places width wise. When you collect the sample from different places, it will give you a better and more accurate gsm of the fabric. In the opening length of a roll, or anywhere a fabric may have been overstretched the fabric will give less gsm value.

**The gsm measurement of a given fabric sample can be done without the gsm cutter. You need a weighing scale, a marker, and a scissor. For this, cut 10/10 cm fabric test specimens and take the weight of these samples using a digital weighing balance. Consider reading weight for 10 samples. To be noted that by using this method you may not get an accurate weight.**


2. Calculate fabric GSM using a formula and fabric construction
In absence of the GSM testing equipment, you can estimate approximate fabric GSM of the fabric sample from the fabric construction. To calculate the fabric GSM from the fabric construction a formula is used by many fabric professionals. The fabric gsm calculation formula is:
Fabric GSM = (EPI/warp count + PPI/Weft count) x (100+crimp %) X 0.2327
This formula is applicable for woven fabric GSM calculation (interlock is knit NOT woven). To use this formula, you need the following technical information.


  • Fabric yarn count - warp count as well as weft yarn count
  • warp and weft density - End per inch (EPI) and picks per inch (PPI)
  • warp and weft crimp percentage
The above technical data of a fabric is not easily available. Other similar formulas are also used (ie. adding in fabric crimp for warp yarns) but often the technical data needed is not easily or accurately available.
GSM Testing Report

In the mass garment manufacturing environment, fabric GSM testing is done during fabric development stage or fabric sourcing stage by the garment manufacturer. Though the gsm is approved at the fabric development, the factory or mill will also test the bulk production fabric.

Sarkar, Prasanta
2018. “What is GSM in Fabric” Online Clothing Study. Published Online 09/06/2018.
By Dawn Jesse and Aimee Snyder. Edited by Sarah Settanni and Jess Lojek