Microfibre is a synethic material and it is cheap. It can absorb a fair amount of urine and it absorbs very quickly.
The downside is that it is prone to compression leaks. It works a bit like a sponge. It can absorb a lot of fluid but press down on it and it will leak.
Microfibre is a good option for day use and around the house. It is not a good idea for long car rides or night time. Pair a microfibre insert with a natural fibre insert like bamboo or hemp for more success!
NEVER put microfibre directly against the skin. It's absorbs moisture so quickly that it will draw all the precious oils from your baby's skin and leave him or her with a terrible nappy rash. Stuff it into a pocket or Weegro sleeve.