Does shirt fabric affect the fit?

I'm contemplating ordering an MTM shirt. To specify the sizing of the shirt, I plan to send in my best-fitting shirt and tweak the measurements slightly. 

Here's my predicament -- I have several shirts which have almost identical measurements, but each fits differently.  In fact, I have two shirts purchased at the same time from the same manufacturer in the same size.  One shirt fits much looser than the other, yet their measurements are identical.

So, the only thing I can conclude is that the fabric of a shirt factors into how a shirt fits.  Is this correct?  If so, how can one specify measurements for an MTM shirt and expect the correct fit if the fit is dependent on the fabric?

Liquidus:

Not sure what type of fabric each shirt.  Other than 100% cotton, no other info is on either shirt.

comrade:

Good point about shrinkage.  But, when I lay the two shirts on top of each other, their measurements are identical, or very close.

Not sure what was meant by, "Delete- That damn bug lives."

Quote:

Originally Posted by bertie 

It seems odd that the measurements are the same but you say they fit differently. All things being equal - same measurements should result in the same fit unless the fabric itself behaves differently when stretched.

The responses to date have focused on shrinkage which is common issue with cotton shirts. Are you implying that there is more stretch/give in one shirt vesus another? Can you elaborate on how they fit differently? is it the neck only, the chest, the arms?

One shirt seems looser in the chest and waist area than the other.  The fabric on the looser shirt is more stiff and therefore balloons out, whereas the fabric on the tighter shirt doesn't.  Not sure how to describe this better.

Quote:

Originally Posted by Liquidus 


You should measure with a tape measure, not lay them on top of each other.

Yes, I will do this and report back.  Currently, I only have a stiff tape measure (for carpentry, etc.).  Will this suffice or must measurements be taken by a more flexible tape measure that's typically used for clothing?

Mystery solved.  Using a tape measure and taking measurements as suggested by propercloth revealed some differences in measurement.  The looser shirt has a neck which is 1/4" larger, and a yoke measurement which is 3/4" larger.  Additionally, the sleeve width is 1/4" larger on the looser shirt.  But, both shirts have the same chest and midsection width which surprised me. Obviously, these differences were not discernible when laying the shirts on top of each other.  By the way, both shirts were made by the lower-cost Joe line of Abboud.

This proved to be an enlightening educational exercise.  Now I know that differences as little as 3/4" can affect the fit of a shirt significantly.  This will help in tweaking measurements for my first MTM shirt.  Thanks for all the suggestions/advice.