Is Lexan a better material to tour with than aluminum based on weight to strenght ratio?

Aluminum is definitely the way to go. I would never use a plastic shovel, and neither would most ski patrollers. Despite however hard or durable a manufacturer may claim a plastic shovel blade is, and no matter how good there warranty is, plastic can crack and break, and aluminum won't. Although engineering and technology has made plastic shovels more durable, they're still not as durable as aluminum. When I took my avy class last year, I remember one of the instructors saying this, "A manufacturers warranty and free replacement won't do me any good when I'm trying to dig out a buried victim and the blade breaks." Those words really stuck with me. The fact of the matter is that is totally true. The extra 15 bucks is definitely worth the peace of mind of knowing you have good, solid, durable gear that will perform when needed. I've never seen a patroller use a plastic blade shovel. That says something about their durability and trustworthiness. Bottom line is when dealing with avalanche safety, you want to do everything to give you (and your buddies) the best chance of survival. With regards to shovels, that means an aluminum blade. Bottom line is that aluminum blades are stronger, will last longer and are pretty light in weight. And however much heavier they may be than a plastic shovel, the weight is going to be unnoticeable in your pack, and you won't have to worry about the blade breaking. Aluminum is definitely stronger than plastic and worth the few extra bucks.

No, I do not think so. A beefy aluminum shovel is always better for digging in avalanche debris. Lexan shovels deflect and have a difficult time punching through hard debris.