How does the sizing run on Holden skinny pants? I'm looking for a pair for my son, who wears a 30x30 skinny jean and can't decide if I should get a small or a medium.

Are these worn alone or over other clothing?

Tech Specs:

Material:

polyester 

Fabric Waterproof Rating:

10000mm 

Fabric Breathability Rating:

5000g/m2 

Fit:

slim 

Venting:

inseam 

Gaiters:

yes 

Seams:

critical taped 

Waist:

belt loops 

Pockets:

2 handwarmer, 2 back zippered 

Recommended Use:

snowboarding 

Manufacturer Warranty:

limited