Two hoodies, both 450gsm, both cotton. One arrives looking like a proper winter piece. The other looks like a mid-season top that someone made heavier for no visible reason. Buyers usually read this as a quality problem. Most of the time it is a specification problem: weight was chosen as a single number, while the thing the buyer actually wanted — how thick the garment feels — depends on the fabric structure behind that number.
What GSM actually measures
GSM is grams per square meter. It measures mass, not thickness, not warmth, and not handfeel. Those three things are related to weight, but they are not the same axis.
A square meter of open, airy knit and a square meter of dense, compacted knit can weigh exactly the same and still behave like two different materials. One is bulky and traps air. The other is thin and firm. Both are "450gsm." If the brief says only "450gsm, winter weight," the mill has to guess which of those you meant — and the guess is usually made by whoever is holding the sample book that day.
This is why weight specifications that look precise often produce samples that get rejected. The number was precise. The requirement behind it was not.
Three variables that move with weight
Weight is one dial. Three others move at the same time, and buyers often treat them as fixed.
Structure. Single knit, loop-back, double knit, and brushed constructions pack the same yarn differently. Loop-back terry holds an open loop on the inside. A brushed fleece has had that loop opened up and raised into pile. The pile adds volume without adding much mass, because the fibers are no longer lying flat against the fabric.
Composition. Cotton, polyester, viscose, and blends have different densities and different bulk. Two fabrics at the same GSM with different fiber content will not feel the same, and they will not drape the same. A cotton-poly blend can feel firmer and more stable than a pure cotton base at the same weight, while a viscose-led knit can feel heavier in the hand than its number suggests.
Finish. Brushing, peach finishing, compacting, and pre-shrinking all change the surface and the density. A brushed surface reads thicker. A compacted surface reads denser and flatter. Neither change shows up in the GSM figure.
Put those three together and the reason becomes obvious: the number on the spec sheet is the starting point of the fabric, not the end result of the garment.
The hoodie case: French terry against French fleece
Hoodies are where this problem shows up most often, because the two most common bases behave differently under the same weight.
French terry is loop-back: a flat face on the outside, an open loop on the inside. The loop is what gives it the soft interior without adding a heavy pile. It stays relatively light for its volume and it breathes, which is why terry can run across seasons rather than sitting only in winter.
French fleece starts from a similar loop-back base, then the inside is brushed. Brushing breaks the loops open and raises the fibers into a pile. The fabric gains bulk. It also gains a softer, warmer surface. The weight barely moves, because brushing rearranges the same fibers rather than adding new ones.
The practical consequence is the part buyers miss:
At the same GSM, a fleece hoodie will look and feel thicker than a terry hoodie.
Not slightly. Noticeably, in the hand and on the body, because the pile is doing work that mass alone does not describe. That single fact changes three decisions that are usually made independently.
Option 1 — keep the silhouette, drop the weight
If the style is a fitted or regular-cut hoodie and the target is a winter feel, fleece at a lower weight can deliver the same visual thickness as terry at a higher weight, with less fabric consumed per garment. The garment looks the same on the body. It costs less to make and less to ship.
Option 2 — keep the weight, open the fit
Because the extra bulk sits inside the same measurements, a fleece hoodie cut to a regular block reads noticeably slimmer than the terry version of the same block — the fabric takes up room that the pattern was not giving back. If the buyer has already committed to a weight number, the way to keep the garment comfortable and on-brief is usually to relax the fit: a boxier body, a slightly wider sleeve, so the bulk reads as intentional rather than as a sizing error. This is often the right answer for oversized and streetwear-led programs.
Option 3 — keep the thickness, raise the terry weight
If the buyer wants terry's flat face and breathability but the visual weight of a fleece piece, terry has to go up in GSM to get there. That is a legitimate choice, but it is a different cost profile: more fabric per garment, a heavier finished piece, and a thicker fabric to handle at the sewing stage.
None of these three is wrong. The problem is picking one by accident.
A comparison at a glance
| 450gsm French terry | 450gsm French fleece | |
|---|---|---|
| Visual thickness | Medium | Noticeably thicker |
| Interior | Open loop, dry hand | Raised pile, soft and warm |
| Breathability | Higher | Lower |
| Best fit language | Regular at the drawn size | Reads one step slimmer at the same cut |
| If you want a slim fit | Cut a slimmer block | The drawn block already reads slim |
| Fabric price at equal weight | Same | Same |
| Fabric used per garment | Baseline | Higher once the block is opened to hold the fit |
Both columns assume the same pattern. That is the point: a thicker fabric occupies more of the same measurement, so a regular block in fleece lands closer to a slim block in terry. If the tech pack asks for a regular fit, the fleece version has to be re-blocked wider, or taken down in weight, to land in the same place on the body.
Read the last row carefully. Choosing fleece so you can lower the weight is not a trick to make a cheaper garment. It is a way to buy the same look with less material, which is why it matters at volume and barely matters on a sample.
What this does to cost
Fabric is priced by weight, so two fabrics at the same GSM cost roughly the same per kilo. The cost difference buyers actually feel is not in the yarn — it is in the consumption.
- A heavier fabric changes the size you are cutting. Cut to the same measurements, a heavier fabric takes up more room on the body: the garment reads tighter, and the size that used to sit right now sits one step smaller. To keep the fit the tech pack asked for, the block has to be opened up.
- An opened block uses more fabric per garment. This is where the cost really moves — not in what the fabric costs per kilo, but in how much of it leaves the cutting table for each piece. The heavier the weight, the more the block has to give back, and the more consumption rises.
- Brushing is an extra process step. Fleece carries a finishing operation that terry does not. That step has its own cost and its own risk — an over-brushed fleece loses surface stability, and an under-brushed one feels like flat terry with a misleading name.
- Every extra sampling round has a cost too — not just the sample itself, but the calendar time. A hoodie program that needs three weight iterations before approval has spent weeks that could have been spent in production.
That last point is the one we try to remove.
How to set the weight in four steps
A workable sequence, in the order that avoids most rework:
- Start from the end use, not the number. Winter outer layer, mid-season layering piece, or all-season basic? That answer decides whether the piece needs visual bulk or breathability.
- Pick the structure before the weight. Terry and fleece are not interchangeable at the same number, so the base should be chosen first. Brushed or unbrushed fleece is a second decision on top of that.
- Set the weight inside a range, not as a point. For hoodies, the bases we work with most often run from 220 to 550gsm, and the choice inside that range follows the structure and the fit language. Treating the weight as a range with a target feel is more useful than treating it as a single number to hit.
- Confirm on the body, not on the swatch. Handfeel on a swatch and appearance on a body are different tests. A swatch tells you the surface. A sample garment tells you whether the weight is right for the silhouette.
How we shorten the confirmation loop
Most of the back-and-forth in a hoodie program comes from one thing: the buyer and the mill are comparing different references. The buyer is looking at a competitor's garment. The mill is looking at a fabric card. Neither one settles the question, so the program goes through another round.
We handle this with two things.
A fabric team that reads weight in context. When a brief says "winter weight, 450gsm," the first thing worth checking is the base — because 450gsm fleece and 450gsm terry are two different garments. Our team works with these bases continuously and can tell you, before sampling, which combination of structure, weight, and fit will produce the result described in the brief, and where the trade-offs sit.
Sample garments at the weight you ask for. Instead of sending one sample and waiting for a rejection, we can prepare the comparison in the weights your brief calls for, using the fabric resources we already hold — so the decision is made by comparing real garments rather than by interpreting a number. Two weights side by side usually ends a discussion that three email threads cannot.
That is the practical difference between choosing a weight and confirming a weight. The first is a specification exercise. The second is what actually gets a program into bulk.
FAQ
Is a higher GSM always warmer?
No. Warmth comes from trapped air as much as from mass. A brushed fleece at a moderate weight can feel warmer than a denser, flatter knit at a higher weight, because the pile holds air. Structure and finish matter as much as the number.
Does 450gsm French terry feel the same as 450gsm French fleece?
No. At equal weight, fleece reads thicker and softer because the inside has been brushed into a pile. If the goal is a winter-weight look in a fitted silhouette, fleece at a lower weight is often the closer match.
Can you match the handfeel of a reference garment?
Often, yes — but the useful way to do it is by comparing samples in the weights your brief calls for rather than by agreeing on a number. Send the reference garment or a clear photo with the target weight, and we will come back with the base and weight that sit closest, and say plainly where an exact match is not realistic.
What weight should a winter hoodie be?
Many winter programs ask for something in the region of 450gsm, but the right number depends on whether the base is terry or fleece and how the fit is cut. The bases we work with most often run from 220 to 550gsm; the useful decision is where inside that range the garment should sit, not whether it clears a threshold.
Choosing a weight is really choosing a set of trade-offs between thickness, warmth, fit, and cost. If you are working through that decision now, send the style reference and target season — we will come back with a weight recommendation and, where it helps, sample garments in the weights your brief calls for so the choice can be made on the body.