Working the regular (summer) wedges in cold (5-15 F degree above) they seem more prone to fracturing. And few that blew back out into shins/knee got a hard cussing at.
Maybe the soft ones are blue to remind you they are for cold or more gentle pounding....
I've gotten a few stitches under the chin because of hard pounding and flying plastic , I've learned that more wedges on the bigger trees that need wedging and working the wedges is a better plan than brute force .
I try and use the harder ones in the summer and softer one in the winter but still manage to break or cut them all , I'm OK with killing one per paying job , I consider them a consumable like fuel and bar oil but do try to make them last .