I use various stretch materials to make the knickers and Singlet Tops that I make.
Because I make full brief knickers I mostly use Cotton Lycra and Bamboo Lycra. They are both 95% Cotton/Bamboo 5% Lycra. I like them as real as possible.
I also use Spandex, Double Brushed Polyester and French Terry. Virtually everything I buy has 4 way stretch.
Cotton Lycra comes in 3 sizes. Lightweight, medium weight and heavy weight. I use Medium weight 90% of the time.
Lightweight is quite thin and very Stretchy. I very rarely use this. Lightweight wear out faster, as they are thinner and lighter.
Medium weight is basically what it says. Nice medium weight with good stretch. Just think your average good T Shirt material, only with 4 way stretch.
Heavy weight is actually a fair bit thicker again than medium weight. It still has a good stretch but fits tighter and will last a lot longer than light or medium weight.
Bamboo Lycra is a medium weight material. It is very soft, lush and quite stretchy. It is 95% Bamboo 5% Lycra. It's amazing to wear and just about puddles, when you drop it.
French Terry is a Medium/Heavy weight material. 95% Cotton 5% Lycra. It has the same kind of stretch as medium weight Cotton Lycra. It is regular cotton lycra on the outside, but the inside is brushed and is like a lighter terry towelling. It is lovely and warm to wear and incredibly comfortable. It lasts for a long time.
Double Brushed Polyester can be light, medium or heavy weight material. It is a spandex/Polyester blend with a very good 4 way stretch. It has had the surface brushed, which gives it a soft, velvety feel to the material. I use cotton inner gussets on the knickers in this material.
Spandex is a combination of polyester and polyurethane. It is bathers/swimmers material. It has a good 4 way stretch. I use them for knickers and Singlet top set. Many people use them as bathers/swimmers.