Within the Shipping Rules there is multiple criteria based on weight. One of these being All Product Weights

This criteria means all products within the order need to follow the criteria, rather than the order as a whole follow the criteria. 

For example 1: 

This would mean that if an order came in with 6 products, each individual product would need to be less than 1kg, regardless if the order as a whole weighs more than 1kg.

For example 2:

All products within the order would each have to weigh 2kg. If an order came in with a weight of 6kg, however it is made up of 3 products all weighing 2kg each, this would match that rule criteria.

There is multiple other options for this specific "All Product Weight" criteria, however all follow the general rule of the products needing to follow a certain weight rule.

Need any help with this? One of our Support Team would be happy to give you a hand!