United OrthoCam Walker Fracture Boot Liner

How tall is the medium sized liner? I have a boot that comes up to my knee. I see it’s available in short and tall but it doesn’t specify

What size is this? I need Small

Will this fit in an aircast? I want the black liner because I painted my gray aircast black and aircast doesn't have a black boot.

What size is this? There is no where to select a size