would you say this jacket fits true to size or runs a little small? I usually wear a small in jackets, but if wear sweaters underneath, should I got a size up?

Tech Specs:

Material:

[Shell] HyVent 2L; [Shell lining] mesh, taffeta in sleeves 

Insulation:

[Snap-in liner] 100g Heatseeker 

Waterproof Rating:

[Shell] not specified 

Breathable Rating:

[Shell] not specified 

Core Venting:

No 

Pockets:

[Shell] 2 dual-entry hand pockets, 1 wrist with goggle cloth, 1 internal goggle, 1 internal media; [Liner] 2 front, 1 internal media 

Seam Taped:

[Shell] yes, fully 

Powder Skirt:

Yes, snap-back 

Hood:

Yes 

Zip-in Compatibility:

Yes, snap-in liner included 

Recommended Use:

Skiing 

Manufacturer Warranty:

Lifetime