The description of the bracers of the entangling blast (Magic Item Compendium 80) (2,000 gp; 1 lb.), in part, says that they
allow you [the wearer] to reduce the damage dealt by your magic to ensnare those affected by it. When you activate these bracers, the next spell you cast or spell-like ability you use deals only half its normal damage; however, any creature damaged by the spell becomes entangled for 1d3 rounds, taking an additional 1 point of damage per level of the spell each round on your turn. This damage is of the same type as normally dealt by the spell (or your choice if the spell deals more than one type of damage). These bracers have no effect on a spell or spell-like ability that doesn’t deal damage.
When the description says, "This damage is of the same type as normally dealt by the spell (or your choice if the spell deals more than one type of damage)," it's talking about damage types, and "[d]amage types include weapon damage (subdivided into bludgeoning, slashing, and piercing) and energy damage (positive, negative, acid, cold, electricity, fire, and sonic)" (Player's Handbook 307). Note that ability damage is not a damage type.
Into thin air
If the DM rules that when the bracers description says the wearer can employ its effects by causing "the next spell [he] cast[s to] deal… only half its normal damage" that it means also ability damage, half of each 1 point of ability damage dealt to each ability score by the 3rd-level Sor/Wiz spell thin air [trans] (Frostburn 105) rounds down to no ability damage, and employing the bracers to modify the spell thin air causes the spell do nothing.
And if the DM rules that the when the bracers description says that the wearer can reduce the damage dealt that the description means damage dealt of a damage type—rather than damage read broadly so as to include ability damage—, employing the bracers to modify the spell thin air also causes the spell to do nothing: the spell deals no damage of any damage type (not even of type added by a later text like the ersatz damage type city that can be added to some spells via the metamagic feat City Magic (Cityscape 59-60)).
This reader suspects the bracers were written with spells like the 1st-level Sor/Wiz spell burning hands [evoc] (PH 207) and the 3rd-level Sor/Wiz spell lightning bolt [evoc] (PH 248) in mind—probably to give some poor evoker a modicum of battlefield control—, with which they work just fine. However, when used in conjunction with a spell like the 1st-level Sor/Wiz spell chill touch [necro] (PH 209) or the aforementioned 3rd-level Sor/Wiz spell thin air, things get messy. Ultimately, ask the DM how the bracers work in his campaign.