The 'polka bot' is a very funky variation on the red rap. Made from 2 layers of fleece it isn't waterproof as such but works by allowing slow evaporation of moisture thus keeping the nappy and baby drier inside.
The polka fleece is slightly lighter weight than the red rap fleece so this may be a cooler option for summer nights.
We also think this will be great on warm summer days when no trousers are required! Just bear in mind that sitting in a pushchair or car seat for extended periods may cause wet to wick through the fleece due to compression against the wet nappy.