HDHMR vs MDF for CNC work, and when neither is right

Medium-density fibreboard has no grain and no voids, which is exactly what a cutter wants.

That homogeneity is why MDF carves cleaner than anything else we run. A ball-nose bit tracing a 3D relief leaves a surface that needs almost no sanding; a fine jaali web comes off the bed with a sharp edge instead of a furry one; and a 6mm rib pitch holds without crumbling. It also takes primer and PU better than any other board here, which matters more than people expect — a painted carving lives or dies on how sharp the shoulder of each cut stays under three coats of finish.

The weakness is water, and it is absolute rather than a matter of degree. MDF is compressed wood fibre and glue; wet it and the fibres swell irreversibly. A splash dries out with a slightly raised edge you can feel. Standing water destroys it. This is why we will not quote MDF for a bathroom wall, a balcony, a planter face or a covered-but-open terrace, even when the drawing asks for it. 18mm MDF is the default for wall panels and jaali; 25mm and 30mm for doors and anything that has to feel solid.

HDHMR: denser, flatter, and it holds a screw

High-density high-moisture-resistant board is made the same way as MDF but pressed harder, with a resin system that tolerates humidity.

Two properties earn it a place. First, it stays flat: an 18mm HDHMR panel spanning 2.4 metres holds its plane where the equivalent MDF would develop a visible bow, which is why free-standing jaali partitions and tall shutters get specified in it. Second, it holds a screw right at the edge — no insert, no pilot-and-pray. Hinges, floor channels, wall cleats and hanging systems all work directly in it, and that is the single biggest reason to pay the premium.

The trade-off is that it is denser, so tooling wears faster and machine time is slightly longer, and the very finest carving is marginally softer than in MDF. "Moisture-resistant" also does not mean waterproof: HDHMR survives a humid Delhi lobby or a semi-open corridor. It does not survive standing water, and we do not specify it as if it did.

WPC: the waterproof panel for outdoor jaali and wet areas

Wood-plastic composite is the only board on this list that genuinely does not care about water.

Balconies, facades, bathroom walls, planter faces, terrace screens, utility areas — anywhere rain, spray or standing water reaches, this is the answer, and there is no second option worth discussing. It is light for its thickness, it never chips at a cut edge, and a waterproof panel for an outdoor jaali in WPC will still be flat in five monsoons.

What you give up is edge crispness. WPC is softer under the cutter, so the edge is rounder than MDF's and fine detail loses definition. We keep jaali webs about 12mm rather than 8mm, and fluting pitch at 30mm and up, because a fine web in WPC will flex. Paint needs the correct key coat first — this is the most common WPC failure we see on site, and it is a finish problem rather than a board problem. Laminate, lacquer and foil go on directly.

Plywood: strength and grain, not carving

Plywood is the strongest engineered board per millimetre and the only sheet material here with real grain, and neither of those helps a carved face.

Cut a fine pattern into ply and two things go wrong: the grain tears on tight internal detail, and every ply line reads as a stripe down the flank of the cut. It is excellent for what it is actually for — frames, substructures, battens, soffits, pergolas, and anything a panel has to hang off. BWP ply and CNC cutting also go together well for coarse outdoor screens where the pattern is chunky enough that grain tear does not show, and marine grade will outlast WPC structurally in an exposed position even if it does not match it for maintenance-free life.

Where the design wants visible timber, veneered ply or a veneered MDF face is a better route than carving into raw ply.

Rubber wood: solid timber, where a board face will not do

Everything else on this page is a sheet. Rubber wood is not — it is solid hardwood, sold as planks and glued-up sections.

That changes what it is for. A board gives you a face; rubber wood gives you a section. Frames, beading, edging, a leg, a nosing, anything that has to be thicker than a sheet or hold a screw driven into its end grain. It machines cleanly on the router at 12mm to 50mm, takes stain and polish well, and the open grain is visible and meant to be — if you wanted a uniform painted surface you would be using MDF.

Two cautions. It is a timber, so it moves: it wants seasoning before machining and sealed edges afterwards, and it belongs indoors. And because it is solid, a wide panel is glued up from strips — the glue lines read under a clear finish, which is either the look you want or the reason to choose something else.

Compact sheet: the one that needs no finishing at all

High-pressure laminate compressed into a solid panel, coloured all the way through. It arrives finished.

Nothing else here survives what compact sheet survives. It is unaffected by steam, standing water or scrubbing, which is why it is the standard for toilet cubicles, lockers, laboratory tops and exterior panels. From 12mm it is self-supporting — a cubicle door needs no frame behind it. Edges are machined and polished rather than banded, and because the colour runs through the sheet a cut edge is part of the finish rather than something to hide.

The trade-offs are density and cost. It is extremely hard on tooling, cuts slower than any board on this page, and carries a price to match, so it is specified where the abuse justifies it and rarely anywhere else. It also takes no paint — the sheet is the finish, so the colour has to be chosen at order stage.

The board follows the job, not the other way round. These are the calls we make most weeks.

• Best material for a CNC jaali, indoors: 12mm or 18mm MDF. It holds the finest web and takes paint best. Go to 18mm HDHMR the moment the screen is free-standing or taller than about 2.4m.
• Jaali outdoors or in a bathroom: WPC, webs kept about 12mm. Marine ply if the pattern is coarse and the screen is structural.
• Parametric wave or rib wall, indoors: 18mm MDF. HDHMR if the panels hang off a rail rather than sitting on a substructure. Details on the parametric wall panel page.
• Fluted TV unit or headboard: 18mm MDF, painted. Fluted WPC only if it is a bathroom or a balcony.
• Main door or pooja door: 30mm HDHMR for the shutter if it is heavy or tall, 30mm MDF if the carving is fine and the door is internal. See 3D CNC doors.
• Signage panel: HDHMR for anything wall-mounted and sizeable, MDF for indoor lettering that will be painted, WPC for outdoors.
• Ceiling ribs and baffles: MDF, kept as thin as the span allows — weight is the constraint, not detail.
• Substructure behind any of the above: plywood. It is the sheet material we would hang a panel off; rubber wood is the one we would make a solid frame from.

If your job is not on that list, send the drawing and we will tell you what we would cut it in and why. There is no charge for the answer, and it takes a couple of minutes by email.