From the Auburn Leather website. Glove leather is chrome tanned (softer, lower tensile strength, but can handle heat and moisture better than alum tanned leather). Laces are alum tanned, which makes the leather stronger and stiffer, but both water and heat (even 115 deg) will start to make it break down and get brittle. Nokona switched to a combo tanned leather for laces because they were getting gloves in for a relace (that were not that old) that had been either left in a hot car too many times or had been given the oven treatment.
CHROME-TANNED LEATHER LACE
Chrome-tanned leather laces are known for their soft, rich feel. Typically used in
footwear, most notably hand-sewn shoes, chrome-tanned laces tend to maintain their
shape, color, and temper (feel) even after exposure to moisture and heat in a hand-sewing
operation.
ALUM-TANNED LEATHER LACE
Alum-tanned (Aluminum) leather laces are much firmer, denser, and have overall
increased strength over chrome-tanned laces. Alum laces are not recommended for us in
hand-sewn shoes where laces would be exposed to moisture and heat, but can be used in
certain footwear applications, such as work boots. Alum laces are most notably used in
sporting goods applications, such as baseball/softball glove lacing as well as lacrosse
sticks.