Summer in the Houston area is HOT, up to 100 degrees! 

Temperatures in parked cars & trucks will range from 130 to 180 degrees, even if the windows are cracked open a little.  Even at  just 79 degrees, a car with a black interior, parked outdoors, can reach 192 degrees! (data: National Safe Kids Campaign)

For that matter, most of the USA experiences heat in the mid-90's or above, for at least part of the summer.

Many darters keep their darts supplies in their vehicles, for convenience in going out to play darts in the eventing.  The down side of this is that all of the plastic parts of darts are affected by the heat. 

A few days or weeks in a car's 150+ degree heat, and flights will start to come apart at the seams.  Plastic shafts will soften & warp, and suddenly nylon shafts won't hold flights as well.  Some darts have rubber grips, and those will deteriorate and become sticky/gummy.  Darts cases that are put together with adhesive will start to come apart, and velcro strips held on with glue will peel off.   

Although there may not be any visible deterioration, plastic and fabric will be damaged by such heat, and that will cause premature failure of those items.  Every year, around the end of summer, many darters experience a sudden rash of flights suddenly coming apart, or nylon shafts that have warped.   Invariably, the items were stored in a hot car all summer.

This is also a problem merchandise from many "briefcase" vendors, who sell supplies at darts bars and league events.  While a darts shop typically keeps its inventory in an air-conditioned building, merchandise carried around in the trunk of a car all the time will be in bad shape by the end of summer.

So, make your flights & shafts last longer by not keeping them in your car.  Or, if you must keep a set or two of darts in the car, at least try to keep most of your extra supplies at home in an air-conditioned environment.