Elastics stretch amount means how much that elastic can stretch. Sewing patterns that use elastics must specify the stretch amount for them.
Stretch factor for fabric means how much the fabric stretches. Stretch factor is measured on DOGS and grain-line.
A quick post for my bra log about bra back types. These are the most common bra back types: leotard, camisole and T-type.
When it comes to knit or stretch fabric the simple straight stitch will not work. That's because the fabric is stretchy while the thread is not (unless of course you sew knits with special elastic thread) and when you pull the fabric the thread breaks.
Every sewist must know about them! When it comes to knit or stretch fabric, these two notions are very important.