At what age should a Schutzhund puppy be introduced to burlap?

I introduce puppies to a wide variety of textures (linen, jute, rubber, leather, etc) from an early age to prevent equipment bias. That doesn't mean I do a ton of play with all of those materials, I just make sure my puppy is comfortable with a lot of different materials and textures. Jute and firehose material can be hard for puppies to grip so I typically don't do a lot of play with those materials until teething is complete.