Duet vs. Cover Diaper

Duet Vs Cover diaper, Bumpadum free size diapers
Both  Duet diapers and Cover diapers fit babies from 5-15 kg. Difference between Duet and Cover diaper is in terms of shell and the absorbent material used.
1. Duet shell has inner lining of microfleece  Cover diaper has no inner fabric lining except for fleece at top and bottom. Duet diaper elastics are gentler as compared to cover diaper shells due to the microfleece inner lining throughout the shell. 
2. Duet diapers insert is a two-part insert made of hemp cotton and cotton terry topped with microfleece. For younger babies only one part of the insert can be used to keep the diaper trim. The stay dry organic cotton insert that comes with Cover diaper has 7 layers of organic cotton and is topped with a layer of microfleece on one side. It is a long insert and can be folded as per your baby's wetting pattern and gives extra absorbency where required. The microfleece layer in both Duet insert and the stay dry insert helps in keeping the baby's bottom dry.
3. The Cover Diaper shell can be air dried and reused in case of only pee by using with a fresh insert set. The inserts and Duet shell all need to be washed before reuse.
4. Duet diaper with two-part insert lasts for 3-4 hrs in daytime and 8-9 hrs in the night. Cover diaper with stay dry organic cotton insert lasts for 3 hrs in daytime and needs to be used with a hemp booster to last through the night. 
All Bumpadum inserts are compatible with these shells.

Your final decision would depend on a) whether you want only stay dry comfort for baby or you want to have the flexibility to choose between stay dry and natural fabric organic cotton touching the baby's skin b) whether you are comfortable reusing the shell c) weight of the baby - if closer to the beginning range of 5 kgs, Cover diapers will be much trimmer.