It seems that the effect is very poor—

A bikini will do. The back looks like a belt, too.

If you are bold, you can wear the same color as ordinary underwear.

If you really don't want to show anything behind your back,

You can attach the sponge pad directly to the clothes.

But the effect is definitely not as good as wearing it.

But if the style of the clothes itself is more complicated,

It is recommended to wear ordinary underwear.