I haven't packed infant formula (we used powder) but I have checked other liquids in my checked bags.

My coworkers gave me the tricks when I first started flying
1. Sqeeze some of the air out of the bottle.
2. Tap the cap well in place.
3. Place in plastic bag and tape that bag around the bottle.
4. Put it in a zip lock bag.

I have had liquids bust but at least they stayed in the plastic and didn't ruin anything else. Usually, though, this did the trick. The reason for squeezing out the air is because bottles expand at altitude.

It's true that the cargo is colder than the cabin but it's not below freezing.

Please be very, very careful with your baggage weight limits as your formula can really add pounds. Especially true if you're flying a "low-cost" or regional company.

I highly recommend weaning your baby to powdered formula for travel. I tried liquid formula only once and never again. It was too heavy to carry and fiddly to fill up the bottles. I did manage to get my fussy drinker on to powdered. What I did was mix the liquid and the powder in increasing amounts until he was drinking all powdered.

I also used the bottles with plastic liners because this meant I only had the nipple and ring to clean. Airplane bathrooms are awful for cleaning baby bottles.

I go more into detail in this non-commercial article;
http://flyingwithchildren.blogspot.com
I'm finally editing some of the glitches!