In my experience, Softbums inserts get super absorbant after being washed about 10 times, nearly bulletproof. I had regular leaks the first week I had them and assumed it was because they were so trim or because I had the legs snugged up improperly. I didn't dare use them at night. Then I started using them at night with doublers and now I trust softbums whenever. Now I know what is going on. They just need 10 washes to get to full absorbancy and with three washes prepping and about 2-3 weeks of usage, you get to that point. My advice is prepare for leaks during the first few weeks, or else add a few extra washes to the prepping period.
I'm writing this today because my little one woke up in the morning soaked through in his softbums, I was surprised and confused until I realized I had accidentally use a brand-new insert in the nighttime diaper (only washed 3 times.) Ooops!