I'm not sure if I'm late to the party but, I thought I'd share my experience with TENA Serenity overnight ultimate pads.

I used to simply cut a slit in my diapers (CVS day night fitted briefs) and double them, but you tend to go through quite a few diapers that way and you don't ever seem to reap the full benefits of the second diaper anyway. On a hunch I decided to use the TENA serenity overnight ultimate pads as boosters seeing as true diaper boosters aren't commonly found in stores.

While I haven't tried true booster pads, I have to say these are quite large, and thick. Even if wetting isn't your thing, I'd imagine you could still appreciate the wonderful fluffy thickness added by these pads.
They're roughly 6inx15in which should fit nicely into any medium or larger adult products. They are backed with what I consider to be a silent, extremely soft plastic back sheet. The absorbent pad is a nice light purple with a blue border, not that anyone but you will ever see it anyway.

They have a strong glue strip down the middle which runs nearly the entire length of the pad. I find it works best to take a razor blade and gently slice down the middle of the strip before removing the paper covering the glue strip and then placing it to your liking in your diaper of choice.

*note*This should be obvious but, don't cut a slit in the pad if you intend to use it in underwear (as they're intended to be used) as that will be a disaster.

They easily double the absorbancy of any store brand diaper. The pads seem to be a great mix of pulp and SAP as they wick extremely fast, yet have little to no press out when maxed out.

According to Northshore Care they hold about 13fl oz. Though in my own personal tests they seem to hold more like 20fl oz (~600ml) if you're up and about and give them time to fully absorb rather than sitting or laying down. Add that to the roughly 20fl oz the CVS diapers hold and you've got a seriously absorbent diaper for less than $1 each.

I bought mine at CVS as I was already there anyway and if I recall they were roughly $14/30pads. The very next day I spotted them at Wal-Mart for about $11/30pads. That comes to roughly $0.37 each. Add that to CVS day/night briefs which range from $0.45 to $0.55 each and you've got a deal.

I've even been able to find the delightfully crinkly plastic backed Depends "protection with tabs" as they're called now in stores, which I discovered absorb roughly a teaspoon of liquid, no SAP at all. Add a TENA pad to this and you have a cheap, fun, go anywhere diaper.

TENA Serenity overnight ultimate pads are a quick, easy solution to add capacity and fluff to diapers for those who prefer to buy diapers in-person at a local store.