The same fabric and yet a different fit
Short answer: The fabric is only half of it. The cut, the density of the knit and the placement of the seams decide how the garment sits, even when the fibre content is identical.
What the cut does
Two garments in the same fabric can be cut to completely different patterns. A narrower pattern gives a closer garment in exactly the same fabric. That is why the percentages on the label do not tell the whole story.
The density of the knit
The same fibre can be knitted loosely or densely. A denser knit is heavier, less see through and stretches less. It feels like a different fabric even though it is not. See bamboo t-shirts for men.
The placement of the seams
A side seam gives shape. Tubular knit without a side seam gives a straight silhouette. Same fabric, two completely different garments. See bamboo clothing for women and bamboo underwear for women.
Frequently asked questions
Can you see it in the fibre information
No. It only says what the fibre is, not how it was used.
So how do you compare
By weight, measurements in centimetres and how the fabric feels in your hand.
Is a high bamboo percentage best
Not in itself. Elastane in small amounts often improves the fit.