A baseball warm up jacket is lightweight outerwear that keeps players warm and loose before games and practices, so muscles stay ready for full-speed play.
Cold muscles throw slower and pull easier. That’s the whole reason a warm up jacket exists: it holds body heat in during the twenty or thirty minutes before a pitcher ever takes the mound. The garment is simple — a lightweight zip layer, usually polyester or nylon, sometimes with spandex for stretch — but the job it does between the dugout and the first pitch is real.
This is team apparel, not protective gear. It shows up in team colors and logos, it comes off right before the first inning, and it is built so a player can stretch, swing, and jog without feeling bundled up.
Why Players Actually Wear Them
Warm muscles perform better and resist injury, and a warm up jacket is the simplest way to hold that warmth while a player waits their turn.
Warming up is a slow process. A pitcher throwing in the bullpen, a hitter waiting on deck, and a fielder going through drills are all working in short bursts with idle stretches in between. Without a layer on top, body temperature drops during those gaps and the muscles tighten back up.
The other half of the answer is mobility. A jacket too heavy for the job restricts the exact shoulder rotation and arm swing a player is trying to prime. The materials matter here. Polyester and nylon keep weight down, moisture-wicking fabrics pull sweat off the skin so a player doesn’t cool down damp, and a touch of spandex lets the fabric move with a throwing motion instead of fighting it.
What Separates a Warm Up Jacket From Other Layers
A warm up jacket is designed for the window before play — warmups, pre-game stretching, and cool-weather practices — rather than for full games or cold-weather fan wear.
The features that show up again and again on team-issued jackets point to that purpose. Zippered pockets hold a phone or a set of keys without spilling during a jog. Adjustable cuffs and hoods let a player seal in heat or vent it. Reflective details help during early or late practices. Team branding turns a functional layer into part of the uniform.
Current team products split along the same lines. Nike’s MLB-licensed full-zip hooded jacket uses Therma-FIT fabric and adds water-repellent and heat-managing properties for rain and cold. New Balance’s Shohei Performance Warm Up Jacket comes in XS through 3XL. Warmup layers are for warmth and movement, not protection — a jacket will not absorb a line drive or a slide.
How to Pick the Right One
Mobility, breathability, and moisture management matter far more than how the jacket looks in a mirror.
Sizing is where most people go wrong. Every brand cuts differently, so a medium in one line is not a medium in another — always measure against that brand’s own chart. New Balance’s sizing steps are the standard approach: measure the chest under the arms at the fullest point, the waist around the natural waist, the hips around the fullest part, and the inseam from the top of the inner thigh to the bottom of the ankle bone while standing.
- Weight: if the jacket limits shoulder rotation or a throwing motion, it is too heavy for warmups.
- Fabric: polyester or nylon for low weight, moisture-wicking construction for damp cool-downs.
- Fit: room through the shoulders and chest without bulk that snags on a swing.
- Weather: a plain lightweight layer for mild days; a water-repellent, heat-managing model for rain and cold.
If you are comparing specific team models side by side, our tested baseball warm up jacket roundup lays out the current options with pricing and sizing.
One note on weather: Nike’s MLB-licensed Dodgers jacket and similar cold-weather models carry water-repellent finishes, which suit rainy or chilly game days. A basic lightweight jacket is still the better call for standard warmups, where breathability beats weatherproofing.
Anyone shopping seriously should start from the New Balance Shohei Performance Warm Up Jacket sizing page for a real measurement walkthrough: New Balance’s warm up jacket sizing guide.
FAQs
Is a warm up jacket the same as a dugout jacket?
They overlap heavily. A dugout jacket is the heavier layer players wear on the bench and in the bullpen during a game, while a warm up jacket is the lighter piece worn during pre-game stretching and throwing. Many team-issued jackets cover both jobs, but the warm up version prioritizes breathability and free movement over insulation.
Can you wear one outside of baseball?
Absolutely. These jackets are lightweight zip layers, so they work for running, coaching, or everyday cool-weather wear. The only thing to watch is fit — baseball cuts leave room through the shoulders and chest, which reads slightly looser than a standard fashion jacket.
Do warm up jackets run true to size?
Not reliably across brands. Sizing varies by manufacturer, so a medium in one line may fit like a large in another. Measure your chest, waist, hips, and inseam, then match those numbers against the specific brand’s chart before ordering.
References & Sources
- New Balance. “Shohei Performance Warm Up Jacket.” Supplies the chest, waist, hips, and inseam measuring steps and the XS–3XL size range.
- Nike. “Los Angeles Dodgers Authentic Collection Men’s Nike Therma-FIT MLB Full-Zip Hooded Jacket.” Documents the Therma-FIT fabric and the water-repellent, heat-managing cold-weather build.
- Nike Team Sports. “Nike Team Baseball Catalog.” Lists the 3/4 Sleeve Hot Jacket (897383) at $80.00 in 100% polyester, sized XS–3XL.