Poffin levels determine how much an aspect (condition) will be affected. Every Berry has a base level, which is the level you would receive if the Poffin were created in 60 seconds.
Poffin levels can be improved by making the Poffin in earlier time, given by the formula:
, where B is the base level, T is the time taken, and M is the sum of burns and spills.
For example, an Aguav Berry has a base level of 14. This means completing in 60 seconds with 0 burns and 0 spills will yield a level 14 Poffin: 14 * 1 = 14. If, however, the Poffin was created in 40 seconds, it would be 14 * 3/2 = 21. The level 21 Poffin then contributes 21 condition stat points upon consumption (assuming a neutral nature).
Although logically this would imply that the higher level is better, this is only true for identical Poffins. This is because Poffins have smoothness which contributes to a Pokémon's sheen level. A Pokémon's sheen cannot exceed 255 and can never be reset. Thus, the choice of Poffins has a big influence on the development of a condition.