That is probably because you're using something like ClearCare which is a buffered hydrogen peroxide (with some other stuff) and a case that acts as a catalyst.

That is probably because you're using something like ClearCare which is a buffered hydrogen peroxide (with some other stuff) and a case that acts as a catalyst. The peroxide sterilizes your contacts, the catalyst slowly converts all the hydrogen peroxide to water. It takes at least 6 hours and you have to change the case out with every new bottle every month or so or else you get hydrogen peroxide in your eyes, which even in small amounts is really awful. I use to use the stuff by choice because it helped my eyes feel more comfortable vs the other contact lens solutions (except for the days I was lazy and didn't change out the cases or over wore my lenses past the X amount of days before disposal). I had soft contacts, that's why it was a choice, but I'm pretty sure hard contacts require the use of this type of cleaning method. Now I use dailies because they're more comfortable even though they're crazy expensive.