The Leah leggings are drafted for fabrics with 70% crosswise and lengthwise stretch with good stretch recovery. Below I'm talking about the shops I've bought fabrics from to help you make a more informed decision when choosing fabrics for your own Leah leggings.
Blue Moon Fabrics
Blue Moon Fabrics have a great selection of active wear and swimwear fabrics. For the Leah leggings I've used their Synergy Polyester Lycra Fabric. This fabric is buttery soft and it feels like you are not wearing anything. At first glance it looks like it has great stretch recovery, but the more you wear it the more it stretches out (especially around the waist). I also noticed that the leggings doesn't return to its original length even after I've washed them.
I love this fabric though and I won't stop buying it, so to work around this I like to make the inner waistband in power mesh or athletic mesh. This make the leggings stay in place all day and the waistband doesn't stretch out because it is stabilized with a mesh fabric that is more compressive.
Greenstyle Fabrics
I have used a few different fabrics from Greenstyle Fabrics and my favorite is their Brushed Yoga fabric. This fabric is more compressive but still very comfortable. It also has great stretch recovery so you don't need a mesh on the inner waistband for them to stay up all day.
Blackbird Fabrics
Blackbird Fabrics don't always have activewear fabrics in stock, but when they do they have some good quality fabrics. I've bought a fabric from them called Matte Activewear Knit and it has great stretch recovery, so no need to use a mesh on the inside of the waistband, the leggings stay up anyway!
I will update this blog post as I try other fabrics that are suited for the Leah leggings. If you have any questions feel free to contact me. Until then, happy sewing!