Nice to see the world warming to wool.

The wool is marginally more weight than plastic (from my kit, all sizes XL or XXL):

Medium Weight Plastic Long Johns Zip Top - 290 gm (9.32 oz)
Medium Weight Merino Wool Long Johns Zip Top - 310 gm (9.97 oz)

Medium Weight Plastic Long Johns Bottom - 230 gm (7.4 oz)
Medium Weight Merino Wool Long Johns Bottoms - 275 gm (8.84 oz)

Heavy Weight Plastic Long Johns Top - 320 gm (10.29 oz)
Heavy Weight Merino Wool Long Johns Top - 290 gm (9.32 oz)

The wool, however, is two to three times the price. Wool also requires a hand wash cycle on the washing machine. To its credit, the wool is warmer when wet or damp, dries quicker, and stuffs smaller.